<PAGE>   1
                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM 10-K

(Mark One)
    [X]     ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
            SECURITIES EXCHANGE ACT OF 1934 (FEE REQUIRED)

                   FOR THE FISCAL YEAR ENDED DECEMBER 31, 1999

                                       OR

    [ ]     TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
            SECURITIES EXCHANGE ACT OF 1934 (NO FEE REQUIRED)

             For the transition period from __________ to __________

                           COMMISSION FILE NO. 2-80930

                        DEL TACO RESTAURANT PROPERTIES I
                       (A California limited partnership)
               (Exact name of registrant specified in its charter)

               CALIFORNIA                              95-3852699
     (State or other jurisdiction of                (I.R.S. Employer
     incorporation or organization)              Identification Number)

       23041 AVENIDA DE LA CARLOTA
        LAGUNA HILLS, CALIFORNIA                          92653
 (Address of principal executive offices)              (Zip Code)

       Registrant's telephone number, including area code: (949) 462-9300

        Securities registered pursuant to section 12(b) of the Act: None

        Securities registered pursuant to section 12(g) of the Act: None

        Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days. Yes [X]  No  [ ]

                       DOCUMENTS INCORPORATED BY REFERENCE

        Portions of the registrant's Form S-11 Registration Statement filed
December 17, 1982 are incorporated by reference into Part IV of this report.

<PAGE>   2
                                     PART I

ITEM 1. BUSINESS

The partnership is a publicly-held limited partnership organized under the
California Uniform Limited Partnership Act. The partnership's General Partner is
Del Taco, Inc., a California corporation ("General Partner"). The partnership
sold 8,751 units totaling $4.375 million through an offering of limited
partnership units from March 1983 through March 1984. The term of the
partnership agreement is until April 30, 2022 unless terminated earlier by means
provided in the partnership agreement.

The business of the partnership is ownership and leasing of restaurants in
California to Del Taco, Inc. The partnership acquired land and constructed six
Mexican-American restaurants for long-term lease to Del Taco, Inc. Each property
is leased for 35 years on a triple net basis. Rent is equal to twelve percent of
gross sales of the restaurants. As of December 31, 1999, the partnership had a
total of six properties leased to Del Taco (Del Taco, in turn, has subleased two
of the restaurants).

The partnership has no full time employees. The partnership agreement assigns
full authority for general management and supervision of the business affairs of
the partnership to the General Partner. The General Partner has a one percent
interest in the profits or losses and distributions of the partnership. Limited
partners have no right to participate in the management or conduct of the
partnership's business affairs.


                                       2
<PAGE>   3
ITEM 2. PROPERTIES

The partnership has acquired six properties with proceeds obtained from the sale
of partnership units:

<TABLE>
<CAPTION>
                                                                                                 Date of
                                                        Date of           Restaurant             Commencement
Address                          City, State            Acquisition       Constructed            of Operation(1)
-------                          -----------            -----------       -----------            ------------
<S>                              <C>                    <C>               <C>                    <C>
Riverside Avenue                 Rialto, CA             September 28,     60 seat with drive     February 12, 1985
                                                        1984              through service
                                                                          window
Elden                            Moreno Valley, CA      March 8, 1985     60 seat with drive     June 30, 1985
Avenue                                                                    through service
                                                                          window
Foothill Boulevard               La Verne, CA           April 16, 1985    60 seat with drive     November 6, 1985
                                                                          through service
                                                                          window
Baseline & Archibald             Rancho Cucamonga, CA   July 10, 1985     60 seat with drive     November 26, 1985
                                                                          through service
                                                                          window
Elkhorn Boulevard                Sacramento, CA         August 22, 1985   60 seat with drive     January 15, 1986
                                                                          through service
                                                                          window
Haven Avenue                     Rancho Cucamonga, CA   September 20,     60 seat with drive     February 14, 1986
                                                        1985              through service
                                                                          window
</TABLE>

(1)   Commencement of operation is the first date Del Taco, Inc., as lessee,
      operated the facility on the site as a Del Taco restaurant.


                                       3
<PAGE>   4
                                     PART II

ITEM 3. LEGAL PROCEEDINGS

The partnership is not a party to any material pending legal proceedings.

ITEM 4. SUBMISSIONS OF MATTERS TO A VOTE OF SECURITY HOLDERS

None.

ITEM 5. MARKET FOR THE PARTNERSHIP'S COMMON EQUITY AND RELATED SECURITY HOLDER
        MATTERS

The partnership sold 8,751 ($4,375,500) limited partnership units during the
public offering period ended March 20, 1984 and currently has 866 limited
partners of record. There is no public market for the trading of the units.
Distributions made by the partnership to the limited partners during the past
three fiscal years are described in Note 6 to the Notes to the Financial
Statements contained under Item 8.


                                       4
<PAGE>   5
ITEM 6. SELECTED FINANCIAL DATA

<TABLE>
<CAPTION>
                                             FOR THE YEAR ENDED DECEMBER 31,
                           1999            1998            1997            1996            1995
                        ----------      ----------      ----------      ----------      ----------
<S>                     <C>             <C>             <C>             <C>             <C>
Rental revenue          $  537,905      $  531,608      $  487,280      $  452,203      $  436,262

Interest and
  other income               4,832           4,924           5,109           2,902           2,729

Net income                 451,648         445,860         403,356         365,387         275,020

Net income
  per limited
  partnership
  unit(1)                    51.09           50.44           45.63           41.34           31.11

Cash distributions
  per limited
  partnership unit           56.29           53.84           49.28           44.82           45.70

Total assets             2,459,643       2,497,164       2,515,808       2,543,173       2,569,140

Long-term
  obligations                 None            None            None            None            None
</TABLE>

(1)   The net income per limited partnership unit was calculated based upon
      8,751 weighted average units outstanding for all years presented.

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS

Liquidity and Capital Resources

The partnership offered limited partnership units for sale between March 1983
and March 1984. 15% of the $4.375 million raised through sale of limited
partnership units was used to pay commissions to brokers and to reimburse the
General Partner for offering costs incurred. Approximately $4 million of the
remaining funds were used to acquire sites and build six restaurants.


                                       5
<PAGE>   6
ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS - (Continued)

The six restaurants leased to Del Taco make up almost all of the income
producing assets of the partnership. Therefore, the business of the partnership
is almost entirely dependent on the success of the Del Taco trade name
restaurants that lease the properties. The success of the restaurants is
dependent on a large variety of factors, including, but not limited to, consumer
demand and preference for fast food, in general, and for Mexican-American food
in particular.

Results of Operations

The partnership owns six properties that are under long-term lease to Del Taco
for restaurant operations (Del Taco, in turn, has subleased two of the
restaurants to Del Taco franchisees, one of which is affiliated with Del Taco).

The following table sets forth rental revenue earned by restaurant for the year:

<TABLE>
<CAPTION>
                                                     YEAR ENDED DECEMBER 31,
                                                  1999        1998        1997
                                                --------    --------    --------
<S>                                             <C>         <C>         <C>
Riverside Avenue, Rialto, CA                    $ 85,753    $ 85,545    $ 80,255

Elden Avenue, Moreno Valley, CA                   81,455      82,084      73,557

Foothill Boulevard, La Verne, CA                 116,168     113,886     105,677

Baseling & Archibald, Rancho Cucamonga, CA        90,805      85,069      73,553

Elkhorn Boulevard, Sacramento, CA                 60,554      55,132      49,752

Haven Avenue, Rancho Cucamonga, CA               103,170     109,892     104,486
                                                --------    --------    --------
          Total                                 $537,905    $531,608    $487,280
                                                ========    ========    ========
</TABLE>

The partnership receives rental revenues equal to 12 percent of gross sales from
the restaurants. The partnership earned rental revenue of $537,905 during the
year ended December 31, 1999, which represents an increase of $6,297 from 1998.
The increase in rental revenue was caused by an increase in sales at the
restaurants under lease.


                                       6
<PAGE>   7
ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATIONS - (Continued)

The following table breaks down general and administrative expenses by type of
expense:

                  PERCENTAGE OF TOTAL GENERAL & ADMIN. EXPENSE

<TABLE>
<CAPTION>
                                                   YEAR ENDED DECEMBER 31,
                                                1999         1998         1997
                                               ------       ------       ------
<S>                                            <C>          <C>          <C>
Accounting fees                                 61.71%       59.86%       60.76%
Distribution of
  information to
  limited partners                              36.60        38.43        37.47
Other                                            1.69         1.71         1.77
                                               ------       ------       ------
                                               100.00%      100.00%      100.00%
                                               ======       ======       ======
</TABLE>

Certain reclassifications have been made to the 1998 and 1997 amounts in the
table above to conform to the current year presentation.

General and administrative costs increased from 1998 to 1999 due to increased
costs for accounting and income tax return preparation. Depreciation expense was
the same in both 1998 and 1999.

Net income increased by $5,788 from 1998 to 1999 due to the increase in revenues
of $6,205 offset by the $417 increase in general and administrative expenses.


                                       7
<PAGE>   8
ITEM 8.  FINANCIAL STATEMENTS

PART I.  INFORMATION


<TABLE>
<CAPTION>
                INDEX                                                   PAGE NUMBER
                -----                                                   -----------
<S>                                                                     <C>
Report of Independent Public Accountants                                       9

Balance Sheets at December 31, 1999 and 1998                                  10

Statements of Income for the years ended December 31, 1999,
  1998 and 1997                                                               11

Statement of Changes in Partners' Equity for the three years ended
  December 31, 1999                                                           12

Statements of Cash Flows for the years ended December 31, 1999,
  1998 and 1997                                                               13

Notes to Financial Statements                                              14-18
</TABLE>


                                       8
<PAGE>   9


                          [Arthur Andersen Letterhead]



REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS



To the Partners of
Del Taco Restaurant Properties, I:


We have audited the accompanying balance sheets of Del Taco Restaurant
Properties I (a California Limited Partnership) as of December 31, 1999 and 1998
and the related statements of income, partners' equity and cash flows for the
years then ended. These financial statements and the schedule referred to below
are the responsibility of the Partnership's management. Our responsibility is to
express and opinion on these financial statements based on our audits.

We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free from
material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement
presentation. We believe that our audits provide a reasonable basis for our
opinion.

In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of Del Taco Restaurant Properties
I as of December 31, 1999 and 1998, and the results of its operations and its
cash flows for the years then ended in conformity with generally accepted
accounting principles.

Our audits were made for the purpose of forming an opinion on the basic
financial statements taken as a whole. The schedule in the index of the
financial statements is presented for purposes of complying with the Securities
and Exchange Commission's rules and is not part of the basic financial
statements. This schedule has been subjected to the auditing procedures applied
in our audits of the basic financial statements and, in our opinion, fairly
states in all material respects, the financial data required to be set forth
therein in relation to the basic financial statements taken as a whole.


/s/ ARTHUR ANDERSEN LLP
------------------------------
ARTHUR ANDERSEN LLP



Orange County, California
March 1, 2000





                                       9
<PAGE>   10
                        DEL TACO RESTAURANT PROPERTIES I

                                 BALANCE SHEETS


<TABLE>
<CAPTION>
                                                           DECEMBER 31,
                                                       1999              1998
                                                    ----------        ----------
<S>                                                 <C>               <C>
                                     ASSETS

CURRENT ASSETS:
   Cash                                             $  170,290        $  162,979
   Receivable from Del Taco, Inc.                       46,970            47,833
   Deposits                                                600               797
                                                    ----------        ----------
       Total current assets                            217,860           211,609
                                                    ----------        ----------

PROPERTY AND EQUIPMENT, at cost:
   Land and improvements                             1,852,482         1,852,482
   Buildings and improvements                        1,013,134         1,013,134
   Machinery and equipment                           1,136,026         1,136,026
                                                    ----------        ----------
                                                     4,001,642         4,001,642
   Less--accumulated depreciation                    1,759,859         1,716,087
                                                    ----------        ----------
                                                     2,241,783         2,285,555
                                                    ----------        ----------
                                                    $2,459,643        $2,497,164
                                                    ==========        ==========

                        LIABILITIES AND PARTNERS' EQUITY

CURRENT LIABILITIES:
   Payable to limited partners                      $   31,001        $   24,702
   Accounts payable                                      7,828             5,703
                                                    ----------        ----------
       Total current liabilities                        38,829            30,405
                                                    ----------        ----------

PARTNERS' EQUITY:
   Limited partners                                  2,156,509         2,201,963
   General Partner-Del Taco, Inc.                      264,305           264,796
                                                    ----------        ----------
                                                     2,420,814         2,466,759
                                                    ----------        ----------
                                                    $2,459,643        $2,497,164
                                                    ==========        ==========
</TABLE>

                          The accompanying notes are an
                  integral part of these financial statements.


                                       10
<PAGE>   11
                        DEL TACO RESTAURANT PROPERTIES I

                              STATEMENTS OF INCOME

<TABLE>
<CAPTION>
                                                  YEAR ENDED DECEMBER 31,
                                              1999          1998          1997
                                            --------      --------      --------
<S>                                         <C>           <C>           <C>
REVENUES:
   Rent                                     $537,905      $531,608      $487,280
   Interest                                    3,729         3,425         3,359
   Other                                       1,103         1,499         1,750
                                            --------      --------      --------
                                             542,737       536,532       492,389
                                            --------      --------      --------
EXPENSES:
   General and administrative                 47,317        46,900        45,261
   Depreciation                               43,772        43,772        43,772
                                            --------      --------      --------
                                              91,089        90,672        89,033
                                            --------      --------      --------
       Net income                           $451,648      $445,860      $403,356
                                            ========      ========      ========
   Net income per limited
      partnership unit                      $  51.09      $  50.44      $  45.63
                                            ========      ========      ========
</TABLE>

                          The accompanying notes are an
                  integral part of these financial statements.


                                       11
<PAGE>   12
                        DEL TACO RESTAURANT PROPERTIES I

                    STATEMENT OF CHANGES IN PARTNERS' EQUITY

                       THREE YEARS ENDED DECEMBER 31, 1999

<TABLE>
<CAPTION>
                                   LIMITED PARTNERS
                                ----------------------        GENERAL
                                UNITS         AMOUNT          PARTNER           TOTAL
                                -----      -----------       ---------       -----------
<S>                             <C>        <C>               <C>             <C>
Balance, December 31, 1996      8,751      $ 2,263,579       $ 265,275       $ 2,528,854

   Net income                      --          399,322           4,034           403,356

   Cash distributions              --         (431,267)         (4,356)         (435,623)
                                -----      -----------       ---------       -----------
Balance, December 31, 1997      8,751        2,231,634         264,953         2,496,587

   Net income                      --          441,401           4,459           445,860

   Cash distributions              --         (471,072)         (4,616)         (475,688)
                                -----      -----------       ---------       -----------
Balance, December 31, 1998      8,751        2,201,963         264,796         2,466,759

   Net income                      --          447,132           4,516           451,648

   Cash distributions              --         (492,586)         (5,007)         (497,593)
                                -----      -----------       ---------       -----------
Balance, December 31, 1999      8,751      $ 2,156,509       $ 264,305       $ 2,420,814
                                =====      ===========       =========       ===========
</TABLE>

                          The accompanying notes are an
                  integral part of these financial statements.


                                       12
<PAGE>   13
                        DEL TACO RESTAURANT PROPERTIES I

                            STATEMENTS OF CASH FLOWS

<TABLE>
<CAPTION>
                                                                       YEAR ENDED DECEMBER 31,
                                                                 1999            1998            1997
                                                               ---------       ---------       ---------
<S>                                                            <C>             <C>             <C>
CASH FLOWS FROM OPERATING ACTIVITIES:

Net income                                                     $ 451,648       $ 445,860       $ 403,356
Adjustments to reconcile net income to net
  cash provided by operating activities:
   Depreciation                                                   43,772          43,772          43,772
   Increase in payable to limited partners                         6,299          12,012           1,371
   Decrease (increase) in receivable from General Partner            863          (5,232)         (4,123)
   Increase (decrease) in accounts payable                         2,125            (828)          3,531
   Decrease (increase) in deposits                                   197            (197)             --
                                                               ---------       ---------       ---------
          Net cash provided by operating activities              504,904         495,387         447,907

CASH FLOWS FROM FINANCING ACTIVITIES:

Cash distributions to partners                                  (497,593)       (475,688)       (435,623)
                                                               ---------       ---------       ---------
Net increase in cash                                               7,311          19,699          12,284

Beginning cash balance                                           162,979         143,280         130,996
                                                               ---------       ---------       ---------
Ending cash balance                                            $ 170,290       $ 162,979       $ 143,280
                                                               =========       =========       =========
</TABLE>

                          The accompanying notes are an
                  integral part of these financial statements.


                                       13
<PAGE>   14
                        DEL TACO RESTAURANT PROPERTIES I

                          NOTES TO FINANCIAL STATEMENTS

                                DECEMBER 31, 1999

NOTE 1 - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

THE PARTNERSHIP: Del Taco Restaurant Properties I (a California limited
partnership) was formed on November 30, 1982, for the purpose of acquiring real
property in California for construction of six Mexican-American restaurants to
be leased under long-term agreements to Del Taco, Inc. (General Partner for
operation under the Del Taco trade name).

BASIS OF ACCOUNTING: The partnership utilizes the accrual method of accounting
for transactions relating to the business of the partnership. Distributions are
made to the general and limited partners in accordance with the provisions of
the partnership agreement (see Note 2).

PROPERTY AND EQUIPMENT: Property and equipment is stated at cost. Depreciation
is computed using the straight-line method over estimated useful lives which are
20 years for land improvements, 35 years for buildings and improvements, and 10
years for machinery and equipment.

The partnership accounts for property and equipment in accordance with Statement
of Financial Accounting Standards (SFAS) No. 121, "Accounting for the Impairment
of Long Lived Assets and for Long Lived Assets to be Disposed of." SFAS 121
requires that long-lived assets be reviewed for impairment whenever events or
changes in circumstances indicate that the carrying value of the asset may not
be recoverable. In evaluating long-lived assets held for use, an impairment loss
is recognized if the sum of the expected future cash flows (undiscounted and
without interest charges) is less than the carrying value of the asset. Once a
determination has been made that an impairment loss should be recognized for
long-lived assets, various assumptions and estimates are used to determine fair
value including, among others, estimated costs of construction and development,
recent sales of comparable properties and the opinions of fair value prepared by
independent real estate appraisers. Long-lived assets to be disposed of are
reported at the lower of carrying amount or fair value less cost to sell.


                                       14
<PAGE>   15
DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999

NOTE 1 - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -
         (CONTINUED)

INCOME TAXES: No provision has been made for federal or state income taxes on
partnership net income, since the partnership is not subject to income tax.
Partnership income is includable in the taxable income of the individual
partners as required under applicable income tax laws. Certain items, primarily
related to depreciation methods, are accounted for differently for income tax
reporting purposes (see Note 5).

NET INCOME PER LIMITED PARTNERSHIP UNIT: Net income per limited partnership unit
is based upon the weighted average number of units outstanding during the period
which amounted to 8,751 for all years presented.

USE OF ESTIMATES: The preparation of the financial statements in conformity with
generally accepted accounting principles requires management to make certain
estimates and assumptions that affect the reported amounts of assets and
liabilities at the date of the financial statements and the reported amounts of
revenues and expenses during the reporting period. Actual results could differ
from those estimates.

NOTE 2 - PARTNERS' EQUITY

Pursuant to the partnership agreement, annual partnership net income is
allocated one percent to the General Partner and 99 percent to the limited
partners. A partnership net loss in any year will be allocated 24 percent to the
General Partner and 76 percent to the limited partners until the losses so
allocated equal income previously allocated. Any additional losses will be
allocated one percent to the General Partner and 99 percent to the limited
partners.

Partnership gains from any sale or refinancing will be allocated one percent to
the General Partner and 99 percent to the limited partners until allocated gains
and profits equal losses. Additional gains will be allocated 24 percent to the
General Partner and 76 percent to the limited partners.

In 1986, the General Partner contributed additional capital of $280,000 to the
partnership in order to provide funds necessary to complete the sixth and final
restaurant.


                                       15
<PAGE>   16
DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999

NOTE 3 - LEASING ACTIVITIES

The partnership leases certain properties for operation of restaurants to Del
Taco, Inc. on a triple net basis. The leases are for terms of 35 years
commencing with the completion of the restaurant facility located on each
property and require monthly rentals equal to 12 percent of the gross sales of
the restaurants. There is no minimum rental under any of the leases. The
partnership had a total of six properties leased as of December 31, 1999, 1998
and 1997, two of which have been subleased to Del Taco franchisees (one of which
is affiliated with Del Taco, Inc.)

The five restaurants operated by or affiliated with Del Taco, for which the
partnership is the lessor, had combined, unaudited sales of $3,725,831,
$3,721,166, and $3,447,723 and unaudited net income of $192,444, $207,430, and
$149,010 for the years ended December 31, 1999, 1998 and 1997, respectively. Net
income by restaurant includes charges for general and administrative expenses
incurred in connection with supervision of restaurant operations and interest
expense. The one restaurant operated by a Del Taco franchisee, for which the
partnership is the lessor, had unaudited sales of $756,708, $708,908 and
$612,943 for the years ended December 31, 1999, 1998 and 1997, respectively.

The Elkhorn Boulevard restaurant in Sacramento, California had unaudited net
losses of $9,658, $13,373 and $13,302 for the years ended December 31, 1999,
1998 and 1997, respectively.

NOTE 4 - RELATED PARTIES

The receivable from Del Taco consists of rent accrued for the month of December
1999. The rent receivable was collected on January 17, 2000.

The General Partner received $5,007 in distributions relating to its one percent
interest in the partnership for the year ended December 31, 1999.

Del Taco, Inc. serves in the capacity of General Partner in other partnerships
which are engaged in the business of operating restaurants, and three other
partnerships which were formed for the purpose of acquiring real property in
California for construction of Mexican-American restaurants for lease under
long-term agreements to Del Taco, Inc. for operation under the Del Taco trade
name.


                                       16
<PAGE>   17
DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999

NOTE 5 - INCOME TAXES

A reconciliation of financial statement net income to taxable income for each of
the periods is as follows:

<TABLE>
<CAPTION>
                                           1999            1998            1997
                                         ---------       ---------       ---------
<S>                                      <C>             <C>             <C>
Net income per financial statements      $ 451,648       $ 445,860       $ 403,356
Excess tax depreciation                       (669)           (670)         (2,265)
                                         ---------       ---------       ---------
Taxable income                           $ 450,979       $ 445,190       $ 401,091
                                         =========       =========       =========
</TABLE>

A reconciliation of partnership equity per the financial statements to net worth
for tax purposes as of December 31, 1999, is as follows:

<TABLE>
<S>                                                                 <C>
Partners' equity per financial statements                           $ 2,420,814

Issue costs of limited partnership units capitalized for tax
  purposes                                                              637,325

Excess tax depreciation                                                (138,672)

Other                                                                       235
                                                                    -----------
Net worth for tax purposes                                          $ 2,919,702
                                                                    ===========
</TABLE>


                                       17
<PAGE>   18
DEL TACO RESTAURANT PROPERTIES I
NOTES TO FINANCIAL STATEMENTS - CONTINUED
DECEMBER 31, 1999

NOTE 6 - CASH DISTRIBUTIONS TO LIMITED PARTNERS

Cash distributions paid to limited partners for the three years ended December
31, 1999 were as follows:

<TABLE>
<CAPTION>
                                          Cash                  Weighted            Number of Units
                                    Distributions per         Average Number        Outstanding at
                                   Limited Partnership          of Units             the End of
Quarter Ended                             Unit                 Outstanding             Quarter
-------------                      -------------------        --------------        ---------------
<S>                                <C>                        <C>                   <C>
December 31, 1996                        $12.63                    8,751                8,751
March 31, 1997                            11.59                    8,751                8,751
June 30, 1997                             11.19                    8,751                8,751
September 30, 1997                        13.87                    8,751                8,751
                                         ------
   Total paid in 1997                    $49.28
                                         ======
December 31, 1997                         14.21                    8,751                8,751
March 31, 1998                            10.82                    8,751                8,751
June 30, 1998                             13.34                    8,751                8,751
September 30, 1998                        15.47                    8,751                8,751
                                         ------
   Total paid in 1998                    $53.84
                                         ======
December 31, 1998                        $15.08                    8,751                8,751
March 31, 1999                            12.92                    8,751                8,751
June 30, 1999                             13.18                    8,751                8,751
September 30, 1999                        15.11                    8,751                8,751
                                         ------
   Total paid in 1999                    $56.29
                                         ======
</TABLE>

Cash distributions per limited partnership unit were calculated based upon the
weighted average number of units outstanding for each quarter and were paid from
operations. Cash distributions for the quarter ended December 31, 1999 amounted
to $15.19 per limited partnership unit and were paid January 28, 2000.


                                       18
<PAGE>   19
                                    PART III

ITEM 9. DISAGREEMENTS ON ACCOUNTING AND FINANCIAL DISCLOSURE

None

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF THE PARTNERSHIP'S GENERAL PARTNER

(a) & (b) The executive officers and directors of the General Partner and their
ages are set forth below:



<TABLE>
<CAPTION>
Name                                            Title                          Age
----                                            -----                          ---
<S>                          <C>                                               <C>
Kevin K. Moriarty            Director, Chairman and Chief Executive
                             Officer                                           53

C. Ronald Petty              President                                         55

Paul W. Hitzelberger         Executive Vice President, Brand Strategy
                             and  Franchise Relations/Development              55

Robert Terrano               Executive Vice President and  Chief
                             Financial Officer                                 44

James D. Stoops              Executive Vice President, Operations              47

Janet D. Simmons             Senior Vice President, Purchasing                 43

Michael L. Annis             Vice President, Secretary and General
                             Counsel                                           53

C. Douglas Mitchell          Vice President and Corporate Controller           49

Timothy A. Hackbardt         Vice President, Marketing                         36

Shirlene Lopez               Vice President, Corporate Development             35
</TABLE>

The above referenced executive officers and directors of the General Partner
will hold office until the annual meeting of its shareholders and directors,
which is scheduled for the later part of 2000.

(c)     None

(d)     No family relationship exists between any such director or executive
        officer of the General Partner.

(e)     The following is an account of the business experience during the past
        five years of each such director and executive officer:


                                       19
<PAGE>   20
Kevin K. Moriarty, Director, Chairman and Chief Executive Officer of Del Taco,
Inc. Mr. Moriarty began his career with Burger King Corporation in 1974 in
Operations Unit Management. In 1983, he was promoted to Area Manager in New
York, and was subsequently promoted to the Regional Vice President, Chicago
Region in 1985. In 1988, he became Executive Vice President and General Manager
of the North Central Division. Mr. Moriarty served in that position until 1990
when he joined Del Taco, Inc. as President and Chief Executive Officer on July
31, 1990. Mr. Moriarty has served as a Director of the General Partner since
1990.

C. Ronald Petty, President of Del Taco, Inc. Mr. Petty began his career in the
restaurant business in 1973 with McDonald's Corporation. He was employed by
McDonald's in a real estate capacity until 1978. For the next 12 years, Mr.
Petty was in various officer positions with Burger King. These positions
included Vice President of Real Estate, Sr. Vice President of Development,
Region Vice President, Sr. Vice President European Operations, President of
International and President of U.S. Mr. Petty served as President of Miami Subs
from 1990-1992; President and CEO of Denny's 1993-1996; President and CEO of
Peter Piper Pizza 1996-1998; President of Del Taco December 1998-present.

Paul W. Hitzelberger, Executive Vice President, Brand Strategy and Franchise
Relations/Development of Del Taco, Inc. He was appointed to his current position
in December 1995. Mr. Hitzelberger has responsibility for franchise development,
relations and training. He also oversees public relations and training for the
corporation. From 1991 to 1995, Mr. Hitzelberger was Executive Vice President,
Marketing of Del Taco, Inc. From September 1988 through September 1989, Mr.
Hitzelberger was Chief Executive Officer of Environmental Marketing Group. Prior
to that, Mr. Hitzelberger was a Vice President of Del Taco, Inc. Prior to
joining Del Taco, Inc., he served as Vice President - Marketing at the
department store division of Lucky Stores, Inc., a major supermarket retailer.
Mr. Hitzelberger received a Master of Business Administration degree from Loyola
University in Chicago, Illinois.

Robert J. Terrano, Executive Vice President and Chief Financial Officer of Del
Taco, Inc. From May 1994 to April 1995, Mr. Terrano served as Chief Financial
Officer for Denny's, Inc. in Spartanburg, S.C. From August 1983 to May 1994, he
served with Burger King Corporation, Miami Florida, in a variety of positions,
most recently as Division Controller. Mr. Terrano joined Del Taco, Inc. in April
1995.

James D. Stoops, Executive Vice President, Operations of Del Taco, Inc. From
1968 to 1991, Mr. Stoops served in a wide variety of Operations positions with
Burger King Corporation with increasing levels of responsibility. In 1985, Mr.
Stoops was appointed Region Vice President/General Manager for the New York
region and served in that position until October of 1990. In January of 1991, he
joined Del Taco, Inc. in his current post.

Janet D. Simmons, Senior Vice President, Purchasing of Del Taco, Inc. From 1979
to 1986, Ms. Simmons was with Denny's Incorporated. She served in the Research
and Development department in a variety of positions until 1982 when she was
promoted to the position of Purchasing Agent. Ms. Simmons was hired in 1986 as
Manager of Contract Purchasing with Carl Karcher Enterprises, a post she held
until March 1990 when she became Vice President, Purchasing for Del Taco, Inc.
Ms. Simmons has a Bachelor of Science degree in Foods and Nutrition from Cal
State Polytechnic University in Pomona, California.


                                       20
<PAGE>   21
Michael L. Annis, Vice President, Secretary and General Counsel of Del Taco,
Inc. From 1981 to 1986 Mr. Annis served as Regional Real Estate Manager and
Director of Real Estate Services with Taco Bell, Inc. In 1986 he served as
Regional General Manager with Quaker State Minit Lube. In January of 1987 Mr.
Annis joined Red Robin International, Inc. as General Counsel and was
subsequently promoted to Vice President/Secretary and later Vice President Real
Estate Development/Secretary and General Counsel, the position he held until
joining Del Taco, Inc. in December of 1993. Mr. Annis received his J.D. Degree
from Whittier College.

C. Douglas Mitchell, Vice President and Corporate Controller. Mr. Mitchell
joined Del Taco, Inc. in August of 1994 as Controller and was promoted to his
current position in January 1996. From 1990 to 1994, Mr. Mitchell was a Senior
Audit Manager with Coopers & Lybrand. Prior to 1990, Mr. Mitchell held various
positions in finance and accounting with the Geneva Companies (a subsidiary of
Chemical Bank), Zaremba Corporation (a real estate developer) and The Dexter
Corporation (an international manufacturer of specialty materials). Mr. Mitchell
has a Bachelor of Science degree with a major in accounting from the University
of Southern California.

Timothy A. Hackbardt, Vice President, Marketing of Del Taco, Inc. Mr. Hackbardt
joined Del Taco, Inc. in November 1999. Prior to then, since November of 1995,
he served as Vice President of Marketing of Taco Time International, Inc.,
Eugene, OR. From September 1994 to November 1995, Mr. Hackbardt was Director of
Marketing for Wok Spirit Chinese Delivery restaurants in Newport Beach, CA. From
December 1992 to September 1994, Mr. Hackbardt was Director of Marketing for
Fosters Freeze International, Inc., San Luis Obispo, CA. Prior to then, Mr.
Hackbardt held various positions in the television and radio industry in sales
and sales management. Mr. Hackbardt is a graduate of Central Michigan University
where he received a Bachelor of Applied Arts, majoring in Broadcast and
Cinematic Arts and minoring in Marketing.

Shirlene Lopez, Vice President, Corporate Development & Design of Del Taco, Inc.
Ms. Lopez began her career with Del Taco in 1978 as an hourly employee and
advanced through the ranks to General Manager in 1984. Ms. Lopez was promoted to
the corporate office in 1989 as Human Resource Manager. In 1994, she was
promoted to Executive Project Manager reporting to the CEO and in 1996, to
Director of Corporate Development in charge of all interior image and design.
Ms. Lopez has held her current position since August 1997.

ITEM 11. MANAGEMENT REMUNERATION AND TRANSACTIONS

The partnership has no executive officers or directors and pays no direct
remuneration to any executive officer or director of its General Partner. The
partnership has not issued any options or stock appreciation rights to any
executive officer or director of its General Partner, nor does the partnership
propose to pay any annuity, pension or retirement benefits to any executive
officer or director of its General Partner. The partnership has no plan, nor
does the partnership presently propose a plan, which will result in any
remuneration being paid to any executive officer or director of the General
Partner upon termination of employment.


                                       21
<PAGE>   22
ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

(a)     No person of record currently owns more than five percent of limited
        partnership units of the partnership, nor was any person known of by the
        partnership to own of record and beneficially, or beneficially only,
        more than five percent of such securities.

(b)     Neither Del Taco, Inc., nor any executive officer or director of Del
        Taco, Inc. owns any limited partnership units of the partnership.

(c)     The partnership knows of no contractual arrangements, the operation or
        the terms of which may at a subsequent date result in a change in
        control of the partnership , except for provisions in the partnership
        agreement providing for removal of the General Partner by holders of a
        majority of the limited partnership units and if a material event of
        default occurs under the financing agreements of the General Partner.

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

(a)     No transactions have occurred between the partnership and any executive
        officer or director of its General Partner.

        During 1999, the following transactions occurred between the partnership
        and the General Partner pursuant to the terms of the partnership
        agreement.

        (1)     The General Partner earned $4,516 as its one percent share of
                the net income of the partnership.

        (2)     The General Partner received $5,007 in distributions relating to
                its one percent interest in the partnership.

(b)     During 1999, the partnership had no business relationships with any
        entity of a type required to be reported under this item.

(c)     Neither the General Partner, any director or officer of the General
        Partner or any associate of any such person, was indebted to the
        partnership at any time during 1999 for any amount in excess of $60,000.

(d)     Not applicable.


                                       22
<PAGE>   23
                                     PART IV

ITEM 14(a)(1) AND (2). EXHIBITS, FINANCIAL STATEMENTS SCHEDULES, AND REPORTS ON
                       FORM 8-K

        Financial statement schedules:

               Schedule III - Real Estate and Accumulated Depreciation

        Financial statement schedules other than those referred to above have
        been omitted because they are not applicable or not required.


(b)     No reports on Form 8-K were filed during the last quarter of 1999.

(c)     Exhibits required by Item 601 of Regulation S-K:

        1.      Incorporated herein by reference, Restated Certificate and
                Agreement of Limited Partnership of Del Taco Restaurant
                Properties I filed as Exhibit 3.01 to Partnership's Registration
                Statement on Form S-11 as filed with the Securities and Exchange
                Commission on December 17, 1982.

        2.      Incorporated herein by reference, Amendment to Restated
                Certificate and Agreement of Limited Partnership of Del Taco
                Restaurant Properties I.

        3.      Incorporated herein by reference, Form of Standard Lease to be
                entered into by partnership and Del Taco, Inc., as lessee, filed
                as Exhibit 10.02 to Partnership's Registration Statement on Form
                S-11 as filed with the Securities and Exchange Commission on
                December 17, 1982.


                                       23
<PAGE>   24
                 DEL TACO RESTAURANT PROPERTIES I - SCHEDULE III
                    REAL ESTATE AND ACCUMULATED DEPRECIATION
                                DECEMBER 31, 1999

<TABLE>
<CAPTION>
                                                                                 Cost capitalized     Gross amount at
                                                          Initial cost            subsequent to        which carried at
                                                           to company              acquisition         close of period
                                               ------------------------------   -----------------     ------------------
                                                   Land           Building &                          Land, buildings &
Description                                       & land           Improve-         Carrying           improvements
(All Restaurants)              Encumbrances    improvements         ments            costs                Total
---------------------          ------------    ------------     -------------   ------------------    -----------------
<S>                            <C>             <C>              <C>             <C>                    <C>
Rialto, CA                        $ --          $  274,837      $   150,310          $ --                $  425,147
Moreno Valley, CA                   --             353,557          193,362            --                   546,919
La Verne, CA                        --             452,423          247,433            --                   699,856
Rancho Cucamonga, CA                --             293,817          160,690            --                   454,507
Sacramento, CA                      --             260,516          142,478            --                   402,994
Rancho Cucamonga, CA                --             217,332          118,861            --                   336,193
                                  ----          ----------      -----------          ----                ----------
                                  $ --          $1,852,482      $ 1,013,134          $ --                $2,865,616
                                  ====          ==========      ===========          ====                ==========
</TABLE>

<TABLE>
<CAPTION>

                                                                                    Life on which
                                                                               depreciation in latest
Description                        Accumulated    Date of          Date           income statement
(All Restaurants)                 depreciation   construction     acquired          is computed
---------------------             ------------   ------------     --------      ---------------------
<S>                               <C>             <C>            <C>           <C>
Rialto, CA                           $ 92,553        1984           1984          20 (LI), 35 (BI)
Moreno Valley, CA                     119,062        1985           1985          20 (LI), 35 (BI)
La Verne, CA                          152,355        1985           1985          20 (LI), 35 (BI)
Rancho Cucamonga, CA                   98,943        1985           1985          20 (LI), 35 (BI)
Sacramento, CA                         87,731        1985           1985          20 (LI), 35 (BI)
Rancho Cucamonga, CA                   73,189        1985           1985          20 (LI), 35 (BI)
                                     --------
                                     $623,833
                                     ========
</TABLE>

<TABLE>
<CAPTION>
                                                                       Accumulate
                                                     Restaurants      Depreciation
                                                     -----------      ------------
<S>                                                  <C>              <C>
Balances at December 31, 1996:                        $2,865,616        $492,517
   Acquisitions                                               --          43,772
   Sales                                                      --              --
                                                      ----------        --------
Balances at December 31, 1997:                         2,865,616         536,289
   Acquisitions                                               --          43,772
   Sales                                                      --              --
                                                      ----------        --------
Balances at December 31, 1998:                         2,865,616         580,061
   Acquisitions                                               --          43,772
   Sales                                                      --              --
                                                      ----------        --------
Balances                                              $2,865,616        $623,833
                                                      ==========        ========
</TABLE>


                                       24

<PAGE>   25
                                   SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the partnership has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.


                                       DEL TACO RESTAURANT PROPERTIES I
                                       --------------------------------
                                       a California limited partnership

                                       Del Taco, Inc.
                                       General Partner


Date March 07, 2000                    Kevin K. Moriarty
     --------------                    -----------------------------------------
                                       Kevin K. Moriarty
                                       Director, Chairman and Chief
                                       Executive Officer


Date March 07, 2000                    Michael L. Annis
     --------------                    -----------------------------------------
                                       Michael L. Annis
                                       Vice President, Secretary and
                                       General Counsel


Date March 07, 2000                    Robert J. Terrano
     --------------                    -----------------------------------------
                                       Robert J. Terrano
                                       Executive Vice President and
                                       Chief Financial Officer


Date March 07, 2000                    C. Douglas Mitchell
     --------------                    -----------------------------------------
                                       C. Douglas Mitchell
                                       Vice President and Corporate Controller


                                       25

<PAGE>   26
                                 EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT
-------
<S>              <C>
  27             Financial Data Schedule
</TABLE>