<PAGE>   1

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                  FORM 10-Q/A


                QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934


      For the Quarter Ended December 31, 1999 Commission File No. 001-10887


                                JENNY CRAIG, INC.
             ------------------------------------------------------
             (Exact name of registrant as specified in its charter)


          DELAWARE                                     33-0366188
  ------------------------               ------------------------------------
  (State of Incorporation)               (I.R.S. Employer Identification No.)


   11355 NORTH TORREY PINES ROAD,  LA JOLLA, CA                 92037
   --------------------------------------------              ----------
     (Address of principal executive offices)                (Zip Code)


        Registrant's telephone number, including area code(858) 812-7000

        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 [ ]

        Number of shares of common stock, $.000000005 par value, outstanding as
        of the close of business on February 10, 2000- 20,688,971.


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This filing is being made solely to correct the presentation of Note 5 of Notes
to Unaudited Consolidated Financial Statements on Page 6 of Form 10-Q for the
quarter ended December 31, 1999.  Due to an error in the conversion of the table
to EDGAR format, certain amounts in the table were presented in incorrect
columns.
<PAGE>   3

ITEM 1.     FINANCIAL STATEMENTS


                       JENNY CRAIG, INC. AND SUBSIDIARIES
                           CONSOLIDATED BALANCE SHEETS
                                ($ in thousands)

<TABLE>
<CAPTION>
                                                                        June 30,       December 31,
                                                                          1999            1999
                                                                        --------       ------------
                                                                                        (unaudited)
<S>                                                                     <C>            <C>
ASSETS
Cash and cash equivalents ......................................        $ 38,864          28,772
Short-term investments .........................................           3,150           3,651
Accounts receivable, net .......................................           1,925           2,099
Inventories ....................................................          18,036          18,250
Prepaid expenses and other assets ..............................           4,795           2,347
                                                                        --------         -------
         Total current assets ..................................          66,770          55,119
Deferred tax assets ............................................          13,406          23,216
Cost of reacquired area franchise rights, net ..................           8,078           7,578
Property and equipment, net ....................................          24,360          26,196
                                                                        --------         -------
                                                                        $112,614         112,109
                                                                        ========         =======

LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable ...............................................        $ 16,393          18,657
Accrued liabilities ............................................          15,110          21,350
Accrual for litigation judgment ................................           8,203           9,211
Deferred service revenue .......................................          10,075           8,539
                                                                        --------         -------
         Total current liabilities .............................          49,781          57,757
Note payable ...................................................           5,336           5,242
Obligation under capital lease .................................              --           2,029
                                                                        --------         -------
         Total liabilities .....................................          55,117          65,028
                                                                        --------         -------
Stockholders' equity:
Common stock $.000000005 par value, 100,000,000 shares
  authorized; 27,580,260 shares issued; 20,688,971 shares
  outstanding at June 30, 1999 and December 31, 1999 ...........              --              --
Additional paid-in capital .....................................          71,622          71,622
Retained earnings ..............................................          56,507          45,115
Accumulated other comprehensive income .........................           4,130           5,106
Treasury stock, at cost;  6,891,289 shares at June 30, 1999
  and December 31, 1999 ........................................         (74,762)        (74,762)
                                                                        --------         -------
         Total stockholders' equity ............................          57,497          47,081
Commitments and contingencies ..................................
                                                                        ========         =======
                                                                        $112,614         112,109
                                                                        ========         =======
</TABLE>

     See accompanying notes to unaudited consolidated financial statements.


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<PAGE>   4

                       JENNY CRAIG, INC. AND SUBSIDIARIES
                 UNAUDITED CONSOLIDATED STATEMENTS OF OPERATIONS
                   ($ in thousands, except per share amounts)


<TABLE>
<CAPTION>
                                                           Three Months Ended               Six Months Ended
                                                               December 31,                   December 31,
                                                          -----------------------         ----------------------
                                                           1998            1999            1998           1999
                                                          -------         -------         -------        -------
<S>                                                       <C>             <C>             <C>            <C>
Revenues:
  Company-owned operations:
    Product sales ................................        $64,193          53,008         139,185        114,509
    Service revenue ..............................          3,869           4,123           7,951          8,276
                                                          -------         -------         -------        -------
                                                           68,062          57,131         147,136        122,785
                                                          -------         -------         -------        -------
  Franchise operations:
    Product sales ................................          5,235           4,327          10,961          9,372
    Royalties ....................................            951             674           1,777          1,476
    Initial franchise fees .......................              5              25               5             35
                                                          -------         -------         -------        -------
                                                            6,191           5,026          12,743         10,883
                                                          -------         -------         -------        -------
        Total revenues ...........................         74,253          62,157         159,879        133,668
                                                          -------         -------         -------        -------
Costs and expenses:
  Company-owned operations:
    Product ......................................         62,394          53,822         131,274        117,782
    Service ......................................          2,786           3,172           5,526          6,228
                                                          -------         -------         -------        -------
                                                           65,180          56,994         136,800        124,010
                                                          -------         -------         -------        -------
  Franchise operations:
    Product ......................................          3,652           3,144           7,715          6,633
    Other ........................................            398             361             816            780
                                                          -------         -------         -------        -------
                                                            4,050           3,505           8,531          7,413
                                                          -------         -------         -------        -------
                                                            5,023           1,658          14,548          2,245
General and administrative expenses ..............          6,176           6,512          12,134         12,798
Litigation judgment ..............................             --             219              --          1,008
Restructuring charge .............................             --           7,512              --          7,512
                                                          -------         -------         -------        -------
       Operating income (loss) ...................         (1,153)        (12,585)          2,414        (19,073)
Other income, net, principally interest ..........            466             308             931            695
                                                          -------         -------         -------        -------
       Income (loss) before taxes ................           (687)        (12,277)          3,345        (18,378)
Income taxes (benefit) ...........................           (270)         (4,667)          1,272         (6,986)
                                                          -------         -------         -------        -------
      Net income (loss) ..........................        $  (417)         (7,610)          2,073        (11,392)
                                                          =======         =======         =======        =======
      Basic and diluted net income (loss) per
          share ..................................        $  (.02)           (.37)            .10           (.55)
                                                          =======         =======         =======        =======
</TABLE>


     See accompanying notes to unaudited consolidated financial statements.


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<PAGE>   5

                       JENNY CRAIG, INC. AND SUBSIDIARIES
                 UNAUDITED CONSOLIDATED STATEMENTS OF CASH FLOWS
                                ($ in thousands)

<TABLE>
<CAPTION>
                                                                                  Six Months Ended
                                                                                    December 31,
                                                                              -----------------------
                                                                                1998           1999
                                                                              -------         -------
<S>                                                                           <C>             <C>
Cash flows from operating activities:
    Net income (loss) ................................................        $ 2,073         (11,392)
    Adjustments to reconcile net income (loss) to net cash
     used in operating activities:
    Depreciation and amortization ....................................          2,701           2,902
    Non-cash portion of restructuring charge .........................             --           1,303
    Provision for deferred income taxes (benefit) ....................         (4,802)         (9,810)
    Loss on write-off of cost of reacquired area franchise rights ....             --              96
    Loss on disposal of property and equipment .......................            203           1,349
   (Increase) decrease in:
              Accounts receivable ....................................            (26)           (174)
              Inventories ............................................         (2,855)           (214)
              Prepaid expenses and other assets ......................          2,264           2,448
   Increase (decrease) in:
              Accounts payable .......................................          4,327           2,264
              Accrued liabilities ....................................         (3,068)          4,310
              Accrual for litigation judgment ........................             --           1,008
              Deferred service revenue ...............................         (1,501)         (1,536)
                                                                              -------         -------
                       Net cash used in operating activities .........           (684)         (7,446)
                                                                              -------         -------

Cash flows from investing activities:
   Purchase of property and equipment ................................         (1,805)         (2,957)
  Purchase of short-term investments .................................         (4,295)         (3,375)
  Proceeds from maturity of short-term investments ...................          3,042           2,874
                                                                              -------         -------
                       Net cash used in investing activities .........         (3,058)         (3,458)
                                                                              -------         -------

Cash flows from financing activities-
   Principal payments on note payable and capital lease obligation....            (95)           (164)
                                                                              -------         -------

Effect of exchange rate changes on cash and cash .....................             15             976
equivalents
                                                                              -------         -------
Net decrease in cash and cash equivalents ............................         (3,822)        (10,092)
Cash and cash equivalents at beginning of period .....................         42,124          38,864
                                                                               ------         -------
Cash and cash equivalents at end of period ...........................        $38,302          28,772
                                                                              =======         =======


Supplemental disclosure of cash flow information:
   Income taxes paid .................................................        $ 3,832           1,464
Supplemental disclosure of investing activities:
   Equipment acquired under capital lease ............................        $    --           2,726
</TABLE>


     See accompanying notes to unaudited consolidated financial statements.


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<PAGE>   6

                       JENNY CRAIG, INC. AND SUBSIDIARIES
              NOTES TO UNAUDITED CONSOLIDATED FINANCIAL STATEMENTS
                                December 31, 1999


1. The accompanying unaudited consolidated financial statements do not include
all of the information and footnotes required by generally accepted accounting
principles for complete financial statements. In the opinion of management, all
adjustments, consisting only of normal recurring adjustments, considered
necessary for a fair presentation have been included. Operating results for any
interim period are not necessarily indicative of the results for any other
interim period or for the full year. These statements should be read in
conjunction with the June 30, 1999 consolidated financial statements.

2. The weighted average number of shares used to calculate basic net income
(loss) per share was 20,688,971 for all periods presented. The impact of
outstanding stock options during the periods presented did not create a
difference between calculated basic net income (loss) per share and diluted net
income (loss) per share. Stock options had the effect of increasing the number
of shares used in the diluted net income per share calculation by application of
the treasury stock method by 5,584 shares for the six months ended December 31,
1998. The effect of 2,389,800 and 2,938,500 stock options have been excluded
from the calculation of diluted net loss per share for the quarter ended
December 31, 1998 and the quarter and six month period ended December 31, 1999,
respectively, as inclusion of the effect of the stock options would have been
antidilutive.

3. Comprehensive income (loss) for the quarters and six months ended December
31, 1998 and 1999 presented below includes foreign currency translation items.
There was no tax expense or tax benefit associated with the foreign currency
items.

<TABLE>
<CAPTION>
                                         Three Months Ended           Six Months Ended
                                             December 31,                December 31,
                                        --------------------         --------------------
                                         1998          1999          1998          1999
                                        -----         ------         -----        -------
<S>                                     <C>           <C>            <C>          <C>
Net income (loss)                       $(417)        (7,610)        2,073        (11,392)
Foreign currency translation
 adjustments                              512            497            15            976
                                        -----         ------         -----        -------
  Comprehensive income (loss)           $  95         (7,113)        2,088        (10,416)
                                        =====         ======         =====        =======
</TABLE>

4. In November 1999, the Company announced a restructuring plan to reduce
annual operating expenses. The plan included the closure of 86 underperforming
Company-owned centres in the United States, which represented 16% of the total
United States Company-owned centres, and a staff reduction of approximately 15%
at the Company's corporate headquarters. All employees were notified in early
November and the centres were closed by November 30, 1999. A charge of
$7,512,000 was recorded in the quarter ended December 31, 1999 in connection
with this restructuring. The charge was comprised of $3,882,000 for lease
termination costs at the 86 centres, $1,563,000 for severance payments to
terminated employees, $1,303,000 for the write-off of fixed assets at the closed
centres, $291,000 for refunds to program participants at the closed centres, and
$473,000 for other closure costs which include sign removals and demolition of
leasehold improvements. The Company does not believe that there will be any
material sub-lease income available with respect to the closed centres due to
the relatively short remaining lease terms on the respective centres, nor does
the Company believe that there will be any material salvage value of the fixed
assets, which consist substantially of leasehold improvements. Of the total
charge of $7,512,000, approximately $6,209,000 will require cash payments and
$1,303,000 represents the non-cash write-off of fixed assets. As of December 31,
1999, the Company had made cash payments of $685,000 for lease termination
costs, $547,000 for severance to terminated employees, $68,000 for refunds to
program participants, and $11,000 for other closure costs. The Company estimates
that the remaining cash payments of approximately $4,898,000, which is the
principal reason for the increase in accrued liabilities on the accompanying
balance sheet at December 31, 1999, will be substantially incurred by June 30,
2000.



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<PAGE>   7

                       JENNY CRAIG, INC. AND SUBSIDIARIES
              NOTES TO UNAUDITED CONSOLIDATED FINANCIAL STATEMENTS
                                   (Continued)


5. The Company operates in the weight management industry. Substantially all
revenue results from the sale of weight management products and services,
whether the centre is operated by the Company or its franchisees. The Company's
reportable segments consist of Company-owned operations and franchise
operations, further segmented by geographic area. The following presents
information about the respective reportable segments ($ in thousands):


<TABLE>
<CAPTION>
                                                Three Months                       Six Months
                                             Ended December 31,                Ended December 31,
                                          ------------------------          -----------------------
                                            1998            1999             1998            1999
                                          --------         -------          -------         -------
<S>                                       <C>              <C>              <C>             <C>
Revenue:
    Company-owned operations:
       United States .............        $ 56,238          44,702          123,725          96,731
       Foreign ...................          11,824          12,429           23,411          26,054
    Franchise operations:
       United States .............           4,888           3,328            9,989           6,874
       Foreign ...................           1,303           1,698            2,754           4,009
Operating income (loss):
    Company-owned operations:
       United States .............          (4,069)        (14,615)          (2,995)        (24,668)
       Foreign ...................           1,796           1,580            3,217           4,107
    Franchise operations:
       United States .............             920             109            1,521             290
       Foreign ...................             200             341              671           1,198
Identifiable assets:
    United States ................          95,501          97,132           95,501          97,132
    Foreign ......................          12,494          14,977           12,494          14,977
</TABLE>



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<PAGE>   8

                                    SIGNATURE


        Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.


                                            JENNY CRAIG, INC.


                                            By: /S/ James S. Kelly
                                               ---------------------------------
                                               James S. Kelly
                                               Vice President and
                                               Chief Financial Officer



Date: March 14, 2000



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