<PAGE>   1

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                    FORM 10-Q


(Mark One)

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

         For the quarterly period ended SEPTEMBER 30, 1999

                                       OR

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

         For the transition period from ________ to _______ .


                        Commission File Number: 000-24193


                          ATLANTIC DATA SERVICES, INC.
             (Exact Name of Registrant as Specified in its Charter)


                  MASSACHUSETTS                         04-2696393
         (State or Other Jurisdiction of             (I.R.S. Employer
         Incorporation or Organization)           Identification Number)


                              ONE BATTERYMARCH PARK
                           QUINCY, MASSACHUSETTS 02169
               (Address of Principal Executive Offices) (Zip Code)

                                (617) 770 - 3333
              (Registrant's Telephone Number, Including Area Code)


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 [   ]

As of November 5, 1999, there were 12,943,346 shares of the Registrant's Common
Stock, $.01 par value per share, outstanding.



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                          ATLANTIC DATA SERVICES, INC.

                                TABLE OF CONTENTS


                                                                            PAGE
                                                                            ----
PART I - FINANCIAL INFORMATION

ITEM 1:  Financial Statements

Condensed Consolidated Balance Sheets as of September 30, 1999
  (Unaudited) and March 31, 1999                                               3

Condensed Consolidated Statements of Income for the Three and Six Months
  Ended September 30, 1999 and 1998 (Unaudited)                                4

Condensed Consolidated Statements of Cash Flows for the Six                    5
  Months Ended September 30, 1999 and 1998 (Unaudited)

Notes to Condensed Consolidated Financial Statements                           6

ITEM 2:  Management's Discussion and Analysis of Financial Condition and
         Results of Operations                                                 9

ITEM 3:  Quantitative and Qualitative Disclosures about Market Risk           15


PART II - OTHER INFORMATION

ITEM 2:  Changes in Securities and Use of Proceeds                            16

ITEM 4:  Submission of Matters to Vote of Security Holders                    16

ITEM 6:  Exhibits and Reports on Form 8-K                                     17


SIGNATURES                                                                    18


EXHIBIT INDEX                                                                 19






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                                     PART I

ITEM 1:  FINANCIAL INFORMATION


                          ATLANTIC DATA SERVICES, INC.
                      Condensed Consolidated Balance Sheets
                      (in thousands, except per share data)

                                                        SEPTEMBER 30,  MARCH 31,
                                                            1999        1999
                                                         -----------   -------
                                                         (Unaudited)
ASSETS
Current assets:
     Cash and cash equivalents                             $37,405     $37,326
     Accounts receivable, net of allowances for doubtful
      accounts of $725 at September 30, 1999 and
      March 31, 1999                                         4,019       7,037
     Prepaid expenses                                          933         100
     Deferred taxes                                            739         739
                                                           -------     -------
         Total current assets                               43,096      45,202
     Property and equipment, net                             1,196       1,346
     Other assets                                              172         213
                                                           -------     -------
TOTAL ASSETS                                               $44,464     $46,761
                                                           =======     =======

LIABILITIES AND STOCKHOLDERS' EQUITY
Current liabilities:
     Accounts payable                                      $   939     $ 1,193
     Accrued expenses and other liabilities                  3,267       4,393
     Income taxes payable                                       --         417
                                                           -------     -------
         Total current liabilities                           4,206       6,003
                                                           -------     -------
Long-term liabilities                                            2          13
                                                           -------     -------

Commitments

Stockholders' equity:
     Preferred stock, $.01 par value, 1,000,000
       authorized, no shares issued or outstanding              --          --
     Common stock, $.01 par value, 60,000,000 shares
       authorized, 13,055,346 shares issued and
       12,943,346 outstanding at September 30,
       1999 and 13,018,391 shares issued and
       12,906,391 outstanding at
       March 31, 1999                                          130         130
     Additional paid-in capital                             26,638      26,526
     Retained earnings                                      13,513      14,114
     Treasury stock (112,000 shares carried at cost)           (25)        (25)
                                                           -------     -------
         Total stockholders' equity                         40,256      40,745
                                                           -------     -------
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY                 $44,464     $46,761
                                                           =======     =======


See accompanying Notes to Condensed Consolidated Financial Statements.



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                          ATLANTIC DATA SERVICES, INC.

                   Condensed Consolidated Statements of Income
                      (in thousands, except per share data)
                                   (Unaudited)



                                            THREE MONTHS ENDED SIX MONTHS ENDED
                                               SEPTEMBER 30,     SEPTEMBER 30,
                                             ----------------  ----------------
                                              1999     1998     1999      1998
                                             -------  -------  -------  -------

Revenues                                     $ 6,789  $18,186  $17,040  $35,633
Cost of revenues                               6,037   10,520   13,617   20,502
                                             -------  -------  -------  -------
Gross profit                                     752    7,666    3,423   15,131
                                             -------  -------  -------  -------
Operating expenses:
     Sales and marketing                         721    1,261    1,400    2,812
     General and administrative                1,812    2,248    3,850    4,553
                                             -------  -------  -------  -------
         Total operating expenses              2,533    3,509    5,250    7,365
                                             -------  -------  -------  -------
Income (loss) from operations                 (1,781)   4,157   (1,827)   7,766
Interest income                                  440      364      846      517
Interest expense                                  (1)      (1)      (1)      (2)
                                             -------  -------  -------  -------
Income (loss) before provision (credit) for
  income taxes                                (1,342)   4,520     (982)   8,281
Provision (credit) for income taxes             (537)   1,955     (381)   3,554
                                             -------  -------  -------  -------
         Net income (loss)                   $  (805) $ 2,565  $  (601) $ 4,727
                                             =======  =======  =======  =======

Basic earnings (loss) per share              $ (0.06) $  0.20  $ (0.05) $  0.39
                                             =======  =======  =======  =======

Diluted earnings (loss) per share            $ (0.06) $  0.19  $ (0.05) $  0.38
                                             =======  =======  =======  =======

Shares used in computing earnings per
  share (basic)                               12,907   12,798   12,907   12,076
                                             =======  =======  =======  =======

Shares used in computing earnings per
  share (diluted)                             12,907   13,226   12,907   12,481
                                             =======  =======  =======  =======



See accompanying Notes to Condensed Consolidated Financial Statements.



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                          ATLANTIC DATA SERVICES, INC.

                 Condensed Consolidated Statements of Cash Flows
                                 (in thousands)
                                   (unaudited)

                                                            SIX MONTHS ENDED
                                                             SEPTEMBER 30,
                                                           ------------------
                                                            1999       1998
                                                           -------    -------

CASH FLOWS FROM OPERATING ACTIVITIES:
Net income                                                 $  (601)   $ 4,727
Adjustments to reconcile net income to net cash provided
 by operating activities:
   Depreciation and amortization                               327        249
   Provision for bad debts                                      --        250
   Change in assets and liabilities:
     Accounts receivable                                     3,018     (4,414)
     Prepaid expenses and other assets                        (792)       139
     Accounts payable                                         (254)       688
     Accrued expenses and other liabilities                 (1,126)       869
     Billings in excess of costs and estimated earnings
      on contracts                                              --        (83)
     Federal and state income taxes                           (417)      (830)
                                                           -------    -------
Net cash provided by operating activities                      155      1,595
                                                           -------    -------

CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment                            (177)      (598)
                                                           -------    -------

CASH FLOWS FROM FINANCING ACTIVITIES:
Principal payments under capital lease obligation              (11)        (9)
Proceeds from exercise of stock options and employee
 stock purchase plan                                           112        417
Net proceeds from initial public offering                       --     23,393
                                                           -------    -------
Net cash provided by financing activities                      101     23,801
                                                           -------    -------

Net increase in cash and cash equivalents                       79     24,798

Cash and cash equivalents, beginning of period              37,326      3,401
                                                           -------    -------

Cash and cash equivalents, end of period                   $37,405    $28,199
                                                           =======    =======

SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Cash paid during the period for:
     Taxes                                                 $   776    $ 4,607
                                                           =======    =======


See accompanying Notes to Condensed Consolidated Financial Statements.



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                          ATLANTIC DATA SERVICES, INC.

              NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS
                                   (Unaudited)
                               September 30, 1999

1.       BASIS OF PRESENTATION

The accompanying unaudited condensed consolidated financial statements have been
prepared by Atlantic Data Services, Inc. (the "Company") in accordance with
generally accepted accounting principles for interim financial information and
with the instructions to Form 10-Q and Article 10 of Regulation S-X.
Accordingly, they 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 solely of normal
recurring adjustments) considered necessary for a fair presentation have been
included. Operating results for the six-month period ended September 30, 1999
are not necessarily indicative of the results that may be expected for future
periods of the full fiscal year. These Condensed Consolidated Financial
Statements should be read in conjunction with the Consolidated Financial
Statements and related notes included in the Company's Annual Report on Form
10-K for the year ended March 31, 1999.

The balance sheet at March 31, 1999 has been derived from the audited financial
statements at that date, but does not include all the information and footnotes
required by generally accepted accounting principles for complete financial
statements.

2.       SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Revenue Recognition

The Company primarily derives its revenue from consulting services under time
and material billing arrangements. Under these arrangements, revenue is
recognized as the services are provided. Deferred revenue pertains to time and
material billing arrangements and represents cash collected in advance of the
performance of services.

Revenue on fixed price contracts is recognized using the percentage of
completion method of accounting and is adjusted monthly for the cumulative
impact of any revision in estimates. The Company determines the percentage of
its contracts by comparing costs incurred to date to total estimated costs.
Contract costs include all direct labor and expenses related to the contract
performance. An asset, "Costs and estimated earnings in excess of billings on
contracts," would represent revenues recognized in excess of amounts billed. The
liability, "Billings in excess of costs and estimated earnings on contracts,"
represents billings in excess of revenues recognized.

Included in revenues are reimbursable contract-related travel and entertainment
expenses, which are separately billed to clients.

Earnings Per Share

The Company follows Statement of Financial Accounting Standards No. 128,
"Earnings Per Share" ("FAS 128"). FAS 128 requires the presentation of two
amounts, basic earnings per share and diluted earnings per share.




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3.       EARNINGS PER SHARE

The following table sets forth the computation of basic earnings per share and
diluted earnings per share for the three and six months ended September 30, 1999
and 1998:

                                                          THREE MONTHS ENDED
                                                            SEPTEMBER 30,
                                                        ---------------------
                                                          1999          1998
                                                        --------      -------
                                                        (in thousands, except
                                                            per share data)
Numerator:
Net income (numerator for basic earnings per
 share and diluted earnings per share)                  $  (805)      $ 2,565
                                                        -------       -------

Denominator:
Denominator for basic earnings per share - weighted
 average shares and special common shares                12,907        12,798
Effect of dilutive securities:
  Employee stock options                                     --           428
                                                        -------       -------
    Denominator for diluted earnings per share -
     adjusted weighted average and assumed
     conversions                                         12,907        13,226
                                                        -------       -------

Basic earnings per share                                $ (0.06)      $  0.20
                                                        =======       =======

Diluted earnings per share                              $ (0.06)      $  0.19
                                                        =======       =======


                                                          SIX MONTHS ENDED
                                                            SEPTEMBER 30,
                                                        ---------------------
                                                          1999          1998
                                                        --------      -------
                                                        (in thousands, except
                                                            per share data)
Numerator:
Net income (numerator for basic earnings per
 share and diluted earnings per share)                  $  (601)      $ 4,727
                                                        -------       -------

Denominator:
Denominator for basic earnings per share - weighted
 average shares and special common shares                12,907        12,076
Effect of dilutive securities:
  Employee stock options                                     --           405
                                                        -------       -------
    Denominator for diluted earnings per share -
     adjusted weighted average and assumed
     conversions                                         12,907        12,481
                                                        -------       -------

Basic earnings per share                                $ (0.05)      $  0.39
                                                        =======       =======

Diluted earnings per share                              $ (0.05)      $  0.38
                                                        =======       =======


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4.       MAJOR CUSTOMERS

The nature of the Company's services results in the Company deriving significant
amounts of revenue from certain customers in a particular period. For the
quarter ended September 30, 1999, two customers accounted for 32.58% and 11.54%
of the Company's revenues. For the quarter ended September 30, 1998, four
customers accounted for 20.12%, 17.78%, 13.64% and 11.54% of the Company's
revenues.



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                          ATLANTIC DATA SERVICES, INC.

ITEM 2:  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
         RESULTS OF OPERATIONS

OVERVIEW

Atlantic Data Services, Inc. ("We" or "ADS") provides information technology
("IT") strategy consulting and systems integration services to customers
exclusively in the financial services industry, primarily banks. Our service
offerings are organized around four primary practice areas: IT Strategy
Consulting, Consolidations and Conversions, Year 2000 Resolution and Electronic
Commerce and Internet Banking.

We were organized in Massachusetts in 1980 to provide consulting services to
banks and bank service bureaus. Our revenues are derived primarily from
professional fees billed to customers on a time and materials basis, or in
certain instances on a fixed price basis. Included in revenues are reimbursable
contract-related travel and entertainment expenses, which are separately billed
to clients. Substantially all of our contracts, other than fixed price
contracts, are terminable by the customer following limited notice and without
significant penalty to the customer. Revenues from fixed price contracts
represented approximately 0% and 5.4% of our revenues for the quarters ended
September 30, 1999 and 1998, respectively.

We have derived, and expect to continue to derive, a significant portion of our
revenues from a relatively limited number of customers. Revenues from our five
largest customers for the quarters ended September 30, 1999 and 1998 were 66.1%
and 69.6%, respectively, as a percentage of revenues. For the quarter ended
September 30, 1999, Fleet Services Corporation, Corillian Corporation, Bank of
Hawaii, UST Data Services, Inc. and SunTrust Corporation accounted for
approximately 32.58%, 11.54%, 8.41%, 7.21% and 6.31%, respectively, of revenues.
For the quarter ended September 30, 1998, National City Corporation, First
Security Information Technology, Inc., Associated Banc-Corp., UST Data Services,
Inc. and Susquehanna Bancshares, Inc. accounted for approximately 20.1%, 17.8%,
13.6%, 11.5% and 6.5%, respectively, of revenues.

Cost of revenues consists primarily of salaries and employee benefits for
personnel dedicated to customer assignments, fees paid to subcontractors for
work performed in connection with customer assignments, and reimbursable
contract-related travel and entertainment expenses incurred by us in connection
with the delivery of our services.

Sales and marketing expenses consist primarily of salaries, employee benefits,
travel expenses and promotional costs. General and administrative expenses
consist primarily of expenses associated with our management, finance and
administrative groups, including recruiting, training, depreciation and
amortization and occupancy costs.

CERTAIN FACTORS THAT MAY AFFECT FUTURE RESULTS

This Report on Form 10-Q includes forward-looking statements. You can identify
these forward-looking statements when you see us using words such as "expect,"
"anticipate," "believe," "intend," "may," "predict," and other similar
expressions. These forward-looking statements cover, among other items: events,
conditions and financial trends that may effect the Company's future plans of
operation, business strategy, growth of operations and financial position,
including statements relating to estimates of earnings for any future financial
period, levels of professional staff and sufficiency of cash and cash equivalent
balances and the Year 2000 issue. Forward-looking statements are not guarantees
of future performance and are necessarily subject to a number of risks and
uncertainties, some of which are




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beyond our control. Actual results could differ materially from those
anticipated as a result of any of the following factors:

-    variations in our revenues and operating results which could cause our
     results of operations to be below the expectations of public market
     analysts and investors;

-    our dependence on the financial services industry;

-    the concentration of our revenues from a relatively limited number of
     customers;

-    our dependence on the Year 2000 market and the current reductions in Year
     2000 spending by our customers;

-    our dependence on key personnel;

-    the availability of professional staff as our business involves the
     delivery of professional services which is labor-intensive;

-    the management of our growth;

-    competition from other companies in the information technology and systems
     integration market;

-    rapid technological change and our ability to develop information
     technology solutions that keep pace with such changes;

-    our potential for contract liability;

-    the risks associated with fixed price contracts;

-    equity control by management;

-    the risks associated with potential acquisitions; and

-    the volatility of our stock price.

Because of these risks and uncertainties, the forward-looking events discussed
in this Report might not transpire.

RECENT DEVELOPMENTS

We continue to experience lower bookings and our financial results have been
affected by the slowdown in merger activity within the banking sector. Further,
many of our clients have completed their use of external resources for their
Year 2000 projects, which has also negatively impacted revenue generation.
Consequently, it is likely that, at least through the remainder of calendar
1999, ADS will continue to experience reduced revenue generation and have
revenue lower than that of the corresponding quarters in the prior fiscal year,
and did for the first two quarters of fiscal year 2000 lower than that of the
immediate preceding quarters. This, in turn, has and will have an adverse impact
on our earnings. Because we are currently committed to maintaining current
staffing levels to support anticipated future customer opportunities we likely
will incur a net loss for the quarter ending December 31, 1999.

VARIABILITY OF QUARTERLY OPERATING RESULTS

Variations in our revenues and operating results have occurred from quarter to
quarter and may continue to occur as a result of a number of factors. Quarterly
revenues and operating results can depend on:

-    the number, size and scope of customer projects commenced and completed
     during a quarter;

-    changes in employee utilization rates;

-    changes in average billing rates;

-    the number of working days in a quarter;

-    the timing of introduction of new service offerings, both by us and our
     competitors;

-    changes in pricing, both by us and our competitors;

-    loss of a significant customer;

-    loss of key personnel;

-    other factors that adversely impact the financial services industry; and



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-    general economic conditions.

The timing of revenues is difficult to forecast because our sales cycle is
relatively long, ranging from one to six months for new projects with existing
customers and three to six months for new customers, and may depend on factors
such as the size and scope of projects or other factors that adversely impact
the financial services industry and general economic conditions. In addition,
the relatively long length of our sales cycle may negatively impact the
operating results for any particular quarter as a result of increased sales and
marketing expenses without associated increases in revenues in the particular
quarter. Furthermore, many of our projects are, and may be in the future,
terminable without customer penalty. An unanticipated termination of a major
project or loss of a major customer could require us to maintain or terminate
underutilized employees, resulting in a higher than expected number of
unassigned persons or higher than expected severance expenses.

QUARTERS ENDED SEPTEMBER 30, 1999 COMPARED TO QUARTER ENDED SEPTEMBER 30, 1998

REVENUES

Revenues decreased 62.7% for the quarter ended September 30, 1999 over the
quarter ended September 30, 1998, from $18.2 million to $6.8 million. This
decrease was primarily due to a decrease in volume of services delivered to
customers and a decrease in our utilization rate. We continue to experience
lower bookings and our financial results have been affected by the slowdown in
merger activity within the banking sector. Further, many of our clients have
completed their use of external resources for their Year 2000 projects, which
has also negatively impacted revenue generation.

COST OF REVENUES

Cost of revenues decreased 42.6% to $6 million from $10.5 million for the
quarter ended September 30, 1999 compared to the quarter ended September 30,
1998, representing 88.9% and 57.9%, respectively, of revenues in each quarter.
The dollar decrease in cost of revenues was primarily due to a decrease in
billable personnel from 321 at September 30, 1998 to 178 at September 30, 1999.
The increase in cost of revenues as a percentage of revenues is due primarily to
decreased utilization rates. Based on current industry conditions, we expect
that decreased utilization rates will continue in fiscal 2000.

SALES AND MARKETING

Sales and marketing expenses decreased 42.8% to $.7 million from $1.3 million
for the quarter ended September 30, 1999 compared to the quarter ended September
30, 1998, representing 10.6% and 6.9% of revenues, respectively. This decrease
resulted primarily from a reduction in our sales and marketing group from 18
employees at September 30, 1998 to 14 employees at September 30, 1999, the
decrease in sales commissions, travel related expenses for the sales group, as
well as decreased investment in marketing initiatives. We expect our sales and
marketing expenses to increase in absolute dollars as we add sales and marketing
staff.

GENERAL AND ADMINISTRATIVE

General and administrative expenses decreased 19.4% to $1.8 million from $2.2
million for the quarter ended September 30, 1999 compared to the quarter ended
September 30, 1998, representing 26.7% and 12.4% of revenues, respectively. The
dollar decrease is primarily due to decreases in recruiting efforts for new
employees. The increase in general and administrative expenses as a percentage
of revenues reflects the significant decrease in revenues for the quarter ended
September 30, 1999 compared to the quarter ended September 30, 1998.



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<PAGE>   12


INTEREST INCOME

Interest income increased $76,000 from $364,000 for the quarter ended September
30, 1998 to $440,000 for the quarter ended September 30, 1999. This increase was
principally due to the increase in the amount of cash and cash equivalents
available for investment because of additional cash generated from operations.

PROVISION (CREDIT) FOR INCOME TAXES

The provision (credit) for income taxes decreased $2.5 million to $(.5) million
from $2.0 million for the quarter ended September 30, 1999 compared to the
quarter ended September 30, 1998, resulting in effective tax rates of (40)% and
43.2%, respectively. The credit is the result of a net operating loss for the
quarter ended September 30, 1999. Our rate may vary from period to period based
on doing business in areas with varying state and local statutory income tax
rates.


SIX MONTHS ENDED SEPTEMBER 30, 1999 AND 1998

REVENUES

Revenues decreased 52.2% for the six months ended September 30, 1999 over the
six months ended September 30, 1998, from $35.6 million to $17 million. This
decrease was primarily due to a decrease in volume of services delivered to
customers and a decrease in our utilization rate. We continue to experience
lower bookings and our financial results have been affected by the slowdown in
merger activity within the banking sector. Further, many of our clients have
completed their use of external resources for their Year 2000 projects, which
has also negatively impacted revenue generation.

COST OF REVENUES

Cost of revenues decreased 33.6% to $13.6 million from $20.5 million for the six
months ended September 30, 1999 compared to the six months ended September 30,
1998, representing 79.9% and 57.5%, respectively, of revenues in each period.
The dollar decrease in cost of revenues was primarily due to a decrease in
billable personnel from 321 at September 30, 1998 to 178 at September 30, 1999.
The increase in cost of revenues as a percentage of revenues is due primarily to
decreased utilization rates. Based on current industry conditions, we expect
that decreased utilization rates will continue in fiscal 2000.

SALES AND MARKETING

Sales and marketing expenses decreased 50.2% to $1.4 million from $2.8 million
for the six months ended September 30, 1999 compared to the six months ended
September 30, 1998, representing 8.2% and 7.9% of revenues, respectively. This
decrease resulted primarily from a reduction in our sales and marketing group
from 18 employees at September 30, 1998 to 14 employees at September 30, 1999,
the decrease in sales commissions, travel related expenses for the sales group,
as well as decreased investment in marketing initiatives. We expect our sales
and marketing expenses to increase in absolute dollars as we add sales and
marketing staff.

GENERAL AND ADMINISTRATIVE

General and administrative expenses decreased 15.4% to $3.9 million from $4.6
million for the six months ended September 30, 1999 compared to the six months
ended September 30, 1998, representing 22.6% and 12.8% of revenues,
respectively. The dollar decrease is primarily due to decreases in



                                       12
<PAGE>   13


recruiting efforts for new employees. The increase in general and administrative
expenses as a percentage of revenues reflects the significant decrease in
revenues for the six months ended September 30, 1999 compared to the six months
ended September 30, 1998.

INTEREST INCOME

Interest income increased $329,000 from $517,000 for the six months ended
September 30, 1998 to $846,000 for the six months ended September 30, 1999. This
increase was principally due to the increase in the amount of cash and cash
equivalents available for investment because of the net proceeds received from
our initial public offering completed on May 28, 1998 of $23.4 million and
additional cash generated from operations.

PROVISION (CREDIT) FOR INCOME TAXES

The provision (credit) for income taxes decreased $3.9 million to $(.4) million
from $3.5 million for the six months ended September 30, 1999 compared to the
six months ended September 30, 1998, resulting in effective tax rates of (38.7)%
and 42.9%, respectively. Our rate may vary from period to period based on doing
business in areas with varying state and local statutory income tax rates.

LIQUIDITY AND CAPITAL RESOURCES

We have no long-term debt and continue to operate primarily debt-free. Working
capital was $38.9 million at September 30, 1999. Our days sales in accounts
receivable at September 30, 1999 was 53 compared to 66 days at September 30,
1998. The decrease in days sales outstanding was the result of increased
emphasis on collections. While we believe that the risk with respect to
collection of accounts receivable is minimized by the creditworthiness of our
customers, primarily banks and other financial institutions, and our credit and
collection policies, there can be no assurance that we will not encounter
collection problems in the future. We attempt to further minimize this risk by
performing ongoing credit valuations of our customers and maintaining an
allowance for potential credit losses. We believe that our allowance for
doubtful accounts and collection policies are adequate.

Capital expenditures for the six months ended September 30, 1999 of $177,000
were primarily to support our existing employees. Capital expenditures for the
remainder of fiscal 2000 are expected to be approximately $350,000 and will be
used principally for computers and other equipment and, to a lesser extent,
leasehold improvements.

We expect that existing cash and cash equivalent balances, together with cash
provided from operations, will be sufficient to meet the Company's working
capital and capital expenditure requirements for at least the next twelve
months.

To date, inflation has not had a material impact on the Company's financial
results.

IMPACT OF YEAR 2000

The Year 2000 issue is the result of computer programs using a two-digit format,
as opposed to four digits, to indicate the year. Computer systems based on a
two-digit format will be unable to interpret dates beyond the year 1999 which
could cause a system failure or other computer errors, leading to disruptions in
operations. The Year 2000 problem affects virtually all computer systems,
processes, and products in all segments of the economy. We are aware of the
issues associated with the Year 2000 issue and believe there are three general
areas of potential exposure: (1) our own service offerings; (2) our internal
informational systems; and (3) the effects of third party compliance efforts.
Based on our analysis through September 30, 1999, we do not believe that the
Year 2000 issue will materially affect our business.



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-    Service Offerings and Products. We believe that our information technology
     ("IT") strategy consulting and systems integration services will not be
     affected by the Year 2000 issue because such IT service offerings do not
     involve computer processes that store or manipulate date-related fields. We
     will continue to monitor newly developed or acquired IT service offerings
     and products for Year 2000 compliance. In the event that any of our
     developed or acquired IT service offerings or products are not Year 2000
     compliant in a timely manner, our sales may decline materially, customers
     and those with whom they do business may assert product liability and other
     claims, and our business, results of operations and financial condition
     would be materially and adversely affected.

-    Internal Information Systems. We have conducted an assessment of our
     information technology systems and non-IT systems (such as voice mail,
     telephone and other systems containing embedded microprocessors). As a
     result of our assessment, we have remediated our voice mail, telephone
     system, corporate workstation computers and their servers, making them Year
     2000 compliant. We determined during this assessment that our mission
     critical focus would be the accounting and finance area. As a result, we
     have scrutinized and tested for Year 2000 compliance both the accounting
     software created by third parties and internally developed time and expense
     reporting and project accounting software applications. For such
     third-party software applications, we have obtained written confirmation
     that the software applications are Year 2000 compliant. The results of the
     independent testing of our third party payroll application (ADP) was
     completed by ADP. We believe that our internally developed applications are
     already Year 2000 compliant and testing of the mission critical areas, as
     outlined above, was completed by June 30, 1999.

     Based on currently available information, expenses to date, plus the
     expenses we believe will be associated with these efforts in the future,
     are not expected to be material and we have provided for the enhancements
     of these systems in our operating and capital budgets for the current
     fiscal year. However, if compliance efforts of which we are not currently
     aware are required and are not completed on time, or if the cost of any
     required updating, modification or replacement of any of our IT systems
     exceeds our estimates, the Year 2000 issue could have a material adverse
     effect on our business, financial condition and results of operations.

-    Effects of Third Party Compliance. In addition to our internal systems, we
     rely on third party relationships in the conduct of our business. For
     example, third party vendors handle the payroll function for us, and we
     also rely on the services of the landlord at our facility,
     telecommunication companies, banks, utilities and commercial airlines,
     among others. We have obtained assurances from our landlord and our
     material vendors and suppliers that there will be no interruption of
     service as a result of the Year 2000 issue. We have prepared contingency
     plans to mitigate the negative effects on us in the event the Year 2000
     issue results in the unavailability of any of these services. However,
     contingency plans developed by us may not prevent a service interruption on
     the part of one or more of our third party vendors or suppliers. In
     addition, the failure on the part of the accounting systems of our clients
     due to the Year 2000 issue could result in a delay in the payment of
     invoices issued by us for services and expenses. A material service
     interruption from a material vendor or supplier or a failure of the
     accounting systems of a significant number of our clients would have a
     material adverse effect on our business, financial condition and results of
     operations.

We have prepared written contingency plans to address failures in our major IT
and non-IT systems. These plans include identification of major systems,
dependencies on third parties, and resources and strategies necessary to restore
operations or work around failures. The failure of our accounting systems
resulting from a Year 2000 related power system outage, particularly at the end
of a fiscal period, could represent a reasonably likely worst case scenario. Our
contingency plan provides for an alternate site that is equipped with back-up
power systems that can support the mission critical areas.



                                       14
<PAGE>   15


The information concerning our Year 2000 compliance effort includes
"forward-looking statements." Such forward-looking statements involve known and
unknown risks, uncertainties, and other factors that may cause actual events or
costs to be materially different than indicated by such forward-looking
statements. These factors include, among others, unanticipated costs of
remediation and replacement of our Year 2000 compliance efforts, our inability
to meet our targeted dates as scheduled and the failure of our material
suppliers and other strategic relationships to ensure Year 2000 compliance. Any
estimates and projections described have been developed by management and are
based on our best judgments together with the information that is available to
date. Due to the many uncertainties surrounding the Year 2000 issue, our
stockholders are cautioned not to place undue reliance on such forward-looking
statements.


ITEM 3:  QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

The following discussion about our market risk disclosures involves
forward-looking statements. Actual results could differ materially from those
projected in the forward-looking statements. As of September 30, 1999, we did
not use derivative financial instruments for speculative or trading purposes.

Interest Rate Risk

We invest our cash in corporate money market accounts and collateralized
repurchase agreements. These securities are not subject to interest rate risk
and will not fall in value if market interest rates increase.

Foreign Currency Exchange Risk

The majority of our sales are denominated in U.S. dollars and take place in
North America. We do not believe foreign currency exchange rates or the
introduction of the Euro will have an impact on us.




                                       15
<PAGE>   16



                                     PART II

                                OTHER INFORMATION

ITEM 2:    CHANGES IN SECURITIES AND USE OF PROCEEDS

           (d)   Use of Proceeds

On May 22, 1998, we commenced an initial public offering ("IPO") of 2,500,000
shares of common stock, par value $.01 per share (the "Common Stock"), pursuant
to our final prospectus dated May 22, 1998 (the "Prospectus"). The Prospectus
was contained in our Registration Statement on Form S-1, which was declared
effective by the Securities and Exchange Commission (SEC File No. 333-48703) on
May 21, 1998. Of the 2,500,000 shares of Common Stock offered, 2,000,000 shares
were offered and sold by us and 500,000 shares were offered and sold by certain
stockholders of ADS. As part of the IPO, certain stockholders of ADS granted the
several underwriters, for whom BancAmerica Robertson Stephens, BT Alex Brown and
Adams, Harkness & Hill, Inc., acted as representatives (the "Representatives"),
an overallotment option to purchase up to an additional 375,000 shares of Common
Stock (the "Underwriters' Option"). The IPO closed on May 28, 1998.

On June 22, 1998, the Representatives, on behalf of the several underwriters,
purchased 375,000 shares of Common Stock from certain stockholders of ADS
pursuant to the exercise of the Underwriters' Option.

The aggregate offering price of the IPO to the public was $32,500,000 (exclusive
of the Underwriters' Option), with proceeds to us and the selling stockholders,
after deduction of underwriting discounts, of $24,180,000 (before deducting
offering expenses payable by us) and $6,045,000, respectively. The aggregate
offering price of the Underwriters' Option exercised was $4,875,000, with
proceeds to the selling stockholders, after deduction of the underwriting
discounts and commissions, of $4,533,750.

The aggregate amount of expenses incurred by us through March 31, 1999 in
connection with the issuance and distribution of the shares of Common Stock
offered and sold in the IPO were approximately $3,084,000, including $2,275,000
in underwriting discounts and approximately $809,000 in other expenses. No
further expenses have been incurred.

None of the expenses paid by us in connection with the IPO or the exercise of
the Underwriters' Option were paid, directly or indirectly, to directors,
officers, persons owning ten percent or more of the our equity securities, or
affiliates of ADS.

The net proceeds to us from the IPO, after deducting underwriting discounts and
commissions and other expenses, were approximately $23,371,000.

From May 21, 1998 through September 30, 1999, we have applied approximately
$1,196,000 of the net proceeds from the IPO to working capital. We invested the
balance of such net proceeds primarily in money market accounts.


ITEM 4:    SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

Our Annual Meeting of Stockholders was held on July 29, 1999. Holders of an
aggregate of 12,906,391 shares at the close of business on June 21, 1999 were
entitled to vote at the meeting. At such meeting, the Company's stockholders
voted as follows:



                                       16
<PAGE>   17


Proposal 1. To elect two directors to Class I of the Company's Board of
Directors, each to serve for a term of three years or until his successor is
elected and qualified.

                                   Total Vote
                       Total Vote   Withheld
                        for Each    for Each                   Broker
   Director Name        Nominee     Nominee    Abstentions   Non-Votes
-------------------   -----------   -------    -----------   ---------

David C. Hodgson      10,853,979    701,235        N/A          N/A

Richard D. Driscoll   10,852,979    702,235        N/A          N/A

Messrs. Lee M. Kennedy and William H. Gallagher will continue to hold office
until the 2000 Annual Meeting of Stockholders or until their successors have
been duly elected and qualified or until their earliest resignation or removal.
Messrs. George F. Raymond and Robert W. Howe will continue to hold office until
the 2001 Annual Meeting of Stockholders or until their successors have been duly
elected and qualified or until their earlier resignation or removal.

Proposal 2: To ratify and approve the Company's Amended and Restated 1997 Stock
Plan, as amended, including an increase in the number of shares of Common Stock
to be reserved for issuance thereunder from 1,500,000 shares to 3,000,000
shares.

     Total Vote for   Total Vote Against   Abstentions for
       Proposal 2         Proposal 2          Proposal 2     Broker Non-Votes
     --------------   ------------------   ---------------   ----------------

       8,662,346           938,607              6,644           1,947,617

Proposal 3. To ratify the selection of the firm of PricewaterhouseCoopers LLP,
independent public accountants, as auditors for the fiscal year ending March 31,
2000.

     Total Vote for   Total Vote Against   Abstentions for
       Proposal 3         Proposal 3          Proposal 3     Broker Non-Votes
     --------------   ------------------   ---------------   ----------------

      11,254,998           294,416              5,800              N/A


ITEM 6:    EXHIBITS AND REPORTS ON FORM 8-K

           (a)   Exhibits

                 10.1 Amended and Restated 1997 Stock Plan, as amended
                 (Incorporated by reference to the Company's Registration
                 Statement on Form S-8 filed September 13, 1999 (File No.
                 333-86997))

                 27.1  Financial data schedule

           (b)   Reports on Form 8-K

                 None.




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<PAGE>   18


                                   SIGNATURES


Pursuant to the requirement 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.


                                     ATLANTIC DATA SERVICES, INC.




Date:  November 12, 1999             By: /s/ Robert W. Howe
                                     ----------------------
                                     Robert W. Howe
                                     Chairman and Chief Executive Officer




Date:  November 12, 1999             By: /s/ Paul K. McGrath
                                     -----------------------
                                     Paul K. McGrath
                                     Senior Vice President and Chief Financial
                                     Officer (Principal Financial and Accounting
                                     Officer)





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<PAGE>   19


                                  EXHIBIT INDEX


                                                                            PAGE
                                                                            ----
10.1 - Amended and Restated 1997 Stock Plan, as amended (Incorporated
       by reference to the Company's Registration Statement on Form S-8
       filed September 13, 1999 (File No. 333-86997))

27.1 - Financial Data Schedule                                               20





                                  19