<PAGE>   1




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


                                    FORM 10-Q


                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 NUMBER 0-20165


                               STERIS CORPORATION
             (Exact name of registrant as specified in its charter)


                   OHIO                                 34-1482024
      (State or other jurisdiction of                  (IRS Employer
      incorporation or organization)                Identification No.)


            5960 HEISLEY ROAD,                         440-354-2600
         MENTOR, OHIO  44060-1834             (Registrant's telephone number,
 (Address of principal executive offices)          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 [   ].


The number of Common Shares outstanding as of December 31, 1999: 67,495,079

================================================================================
<PAGE>   2



PART I         FINANCIAL INFORMATION



                               STERIS CORPORATION
                     CONSOLIDATED CONDENSED BALANCE SHEETS
                           (IN THOUSANDS) (UNAUDITED)

================================================================================
<TABLE>
<CAPTION>
                                                                                 DECEMBER 31,        MARCH 31,
                                                                                    1999                1999
                                                                                 ---------           ---------
<S>                                                                              <C>                 <C>
ASSETS
Current assets:
  Cash and cash equivalents                                                      $  28,580           $  23,680
  Accounts receivable                                                              224,400             230,346
  Inventories                                                                      130,225              99,279
  Current portion of deferred income taxes                                          21,910              21,910
  Prepaid expenses and other assets                                                 18,127              18,182
                                                                                 ---------           ---------
TOTAL CURRENT ASSETS                                                               423,242             393,397
Property, plant, and equipment                                                     422,264             372,386
Accumulated depreciation                                                          (134,742)           (111,105)
                                                                                 ---------           ---------
  Net property, plant, and equipment                                               287,522             261,281
Intangibles                                                                        283,336             280,750
Accumulated amortization                                                           (77,598)            (72,499)
                                                                                 ---------           ---------
  Net intangibles                                                                  205,738             208,251
Other assets                                                                         3,444               3,067
                                                                                 ---------           ---------
TOTAL ASSETS                                                                     $ 919,946           $ 865,996
                                                                                 =========           =========

LIABILITIES AND SHAREHOLDERS' EQUITY
Current liabilities:
  Current portion of long-term indebtedness                                      $   1,816           $   2,200
  Accounts payable                                                                  48,695              47,431
  Accrued expenses and other                                                       100,424             107,506
                                                                                 ---------           ---------
TOTAL CURRENT LIABILITIES                                                          150,935             157,137
Long-term indebtedness                                                             265,925             221,500
Deferred income taxes                                                                2,810               2,810
Other long-term liabilities                                                         48,997              48,612
                                                                                 ---------           ---------
TOTAL LIABILITIES                                                                  468,667             430,059
Shareholders' equity:
Serial preferred shares, without par value, 3,000 shares authorized; no
  shares outstanding
Common Shares, without par value, 300,000 shares authorized; issued and
  outstanding shares of 67,495 at December 31, 1999, and 67,956 at
  March 31, 1999, excluding 1,081 and 523 treasury shares, respectively            204,256             222,946
Retained earnings                                                                  254,541             219,863
Cumulative translation adjustment                                                   (7,518)             (6,872)
                                                                                 ---------           ---------
TOTAL SHAREHOLDERS' EQUITY                                                         451,279             435,937
                                                                                 ---------           ---------
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY                                       $ 919,946           $ 865,996
                                                                                 =========           =========
</TABLE>

See notes to consolidated condensed financial statements.



                                        2

<PAGE>   3




                               STERIS CORPORATION
                   CONSOLIDATED CONDENSED STATEMENTS OF INCOME
              (IN THOUSANDS, EXCEPT PER SHARE AMOUNTS) (UNAUDITED)

================================================================================

<TABLE>
<CAPTION>
                                                     THREE MONTHS ENDED                NINE MONTHS ENDED
                                                         DECEMBER 31                      DECEMBER 31
                                                 -------------------------       -------------------------
                                                   1999            1998            1999            1998
                                                 ---------       ---------       ---------       ---------

<S>                                              <C>             <C>             <C>             <C>
Net revenues                                     $ 195,119       $ 205,794       $ 570,534       $ 570,694
Cost of goods and services sold                    108,038         109,260         310,840         303,342
                                                 ---------       ---------       ---------       ---------
Gross profit                                        87,081          96,534         259,694         267,352

Costs and expenses:
 Selling, informational, and administrative         61,054          49,793         177,339         150,017
 Research and development                            5,812           6,150          17,735          18,253
                                                 ---------       ---------       ---------       ---------
                                                    66,866          55,943         195,074         168,270
                                                 ---------       ---------       ---------       ---------

Income from operations                              20,215          40,591          64,620          99,082
Interest expense                                    (4,086)         (3,097)        (11,482)         (7,816)
Interest income and other                            1,507             170           2,755             685
                                                 ---------       ---------       ---------       ---------
Income before income taxes                          17,636          37,664          55,893          91,951
Income tax expense                                   6,701          14,689          21,215          35,860
                                                 ---------       ---------       ---------       ---------
Net income                                       $  10,935       $  22,975       $  34,678       $  56,091
                                                 =========       =========       =========       =========

Net income per share - basic                     $    0.16       $    0.34       $    0.51       $    0.82
                                                 =========       =========       =========       =========
Net income per share - diluted                   $    0.16       $    0.33       $    0.51       $    0.79
                                                 =========       =========       =========       =========
</TABLE>

See notes to consolidated condensed financial statements.



                                        3

<PAGE>   4




                               STERIS CORPORATION
                 CONSOLIDATED CONDENSED STATEMENTS OF CASH FLOWS
                           (IN THOUSANDS) (UNAUDITED)

================================================================================
<TABLE>
<CAPTION>
                                                                       NINE MONTHS ENDED
                                                                           DECEMBER 31
                                                                  --------------------------
                                                                     1999            1998
                                                                  ---------       ---------
<S>                                                               <C>             <C>
OPERATING ACTIVITIES
Net income                                                        $  34,678       $  56,091
Adjustments to reconcile net income to
 net cash provided by operating activities:
 Depreciation and amortization                                       30,107          22,882
 Deferred income taxes                                                    0          (7,358)
 Other items                                                           (748)           (270)
 Changes in operating assets and liabilities:
   Accounts receivable                                                6,510          (1,033)
   Inventories                                                      (30,946)        (22,809)
   Other assets                                                       4,515          (3,493)
   Accounts payable and accruals                                     (6,150)         (5,365)
                                                                  ---------       ---------
NET CASH PROVIDED BY OPERATING ACTIVITIES                            37,966          38,645

INVESTING ACTIVITIES
Purchases of property, plant, equipment, and patents                (49,828)        (52,014)
Investment in businesses                                             (6,259)        (48,452)
                                                                  ---------       ---------
NET CASH USED IN INVESTING ACTIVITIES                               (56,087)       (100,466)

FINANCING ACTIVITIES
Payments on long-term obligations                                    (1,659)         (1,114)
Borrowing under credit facility                                      45,000          60,000
Purchase of treasury shares                                         (28,712)         (6,746)
Stock option and other equity transactions                            8,193           7,003
                                                                  ---------       ---------
NET CASH PROVIDED BY FINANCING ACTIVITIES                            22,822          59,143
Effect of exchange rate changes on cash and cash equivalents            199             519
                                                                  ---------       ---------
INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                      4,900          (2,159)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                     23,680          17,172
                                                                  ---------       ---------
CASH AND CASH EQUIVALENTS AT END OF PERIOD                        $  28,580       $  15,013
                                                                  =========       =========
</TABLE>

See notes to consolidated condensed financial statements.

                                       4
<PAGE>   5

                               STERIS CORPORATION
              NOTES TO CONSOLIDATED CONDENSED FINANCIAL STATEMENTS
          (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS) (UNAUDITED)


 PERIODS ENDED DECEMBER 31, 1999 AND 1998

  A. - REPORTING ENTITY

  STERIS Corporation (the "Company" or "STERIS") develops, manufactures, and
  markets infection prevention, contamination prevention, microbial reduction,
  and therapy support systems, products, services, and technologies for health
  care, scientific, research, food, and industrial Customers throughout the
  world. The Company has over 4,700 Associates (employees) worldwide, including
  more than 1,900 direct sales, service, field, and Customer support personnel.
  Customer Support facilities are located in major global market centers with
  production operations in the United States, Australia, Canada, Germany,
  Finland, and Sweden. STERIS operates in a single business segment.

  B. - BASIS OF PRESENTATION

  The accompanying unaudited consolidated condensed financial statements have
  been prepared 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; they do not include all of the information and
  footnotes required by generally accepted accounting principles for complete
  financial statements. Accordingly, the reader of these financial statements
  should refer to the audited consolidated financial statements of STERIS filed
  with the Securities and Exchange Commission as part of STERIS's Form 10-K for
  the year ended March 31, 1999.

  The accompanying consolidated condensed financial statements have been
  prepared in accordance with STERIS's customary accounting practices and have
  not been audited. Management believes that the financial information included
  herein reflects all adjustments necessary for a fair presentation of interim
  results and all such adjustments are of a normal and recurring nature. The
  interim results reported are not necessarily indicative of the results to be
  expected for the fiscal year ending March 31, 2000.

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

  The consolidated financial statements include the accounts of the Company and
  its wholly-owned subsidiaries. Intercompany accounts and transactions have
  been eliminated upon consolidation.

                                       5

<PAGE>   6


                               STERIS CORPORATION
              NOTES TO CONSOLIDATED CONDENSED FINANCIAL STATEMENTS
          (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS) (UNAUDITED)

  C. - EARNINGS PER SHARE

  Following is a summary, in thousands, of Common Shares and Common Share
  equivalents outstanding used in the calculations of earnings per share:


<TABLE>
<CAPTION>
                                                         THREE MONTHS ENDED                        NINE MONTHS ENDED
                                                             DECEMBER 31                              DECEMBER 31
                                               -------------------------------------    -------------------------------------
                                                     1999                  1998               1999                  1998
                                               ---------------       ---------------    ---------------       ---------------
<S>                                                     <C>                   <C>                <C>                   <C>
    Weighted average Common
    Shares outstanding - basic                          67,495                68,174             67,484                68,203
    Dilutive effect of stock options                       893                 2,204              1,156                 2,398
                                               ---------------       ---------------    ---------------       ---------------
    Weighted average Common
    Shares and equivalents - diluted                    68,388                70,378             68,640                70,601
                                               ===============       ===============    ===============       ===============
</TABLE>


  D. - COMPREHENSIVE INCOME

  Comprehensive income amounted to $10,240 and $23,493, net of tax, for the
  quarters ended December 31, 1999 and 1998, respectively. Comprehensive income
  amounted to $34,032 and $56,610, net of tax, for the nine months ended
  December 31, 1999 and 1998, respectively. The entire difference between net
  income and comprehensive income for the periods presented results from changes
  in the cumulative translation adjustment.

  E. - INVENTORIES

  Inventories were as follows:


<TABLE>
<CAPTION>
                                                                    DECEMBER 31,                  MARCH 31,
                                                                        1999                         1999
                                                              -----------------------      ----------------------
<S>                                                                           <C>                         <C>
  Raw material                                                                $41,080                     $36,878
  Work in process                                                              31,905                      19,585
  Finished goods                                                               57,240                      42,816
                                                              -----------------------      ----------------------
                                                                             $130,225                     $99,279
                                                              =======================      ======================
</TABLE>


                                       6
<PAGE>   7


                               STERIS CORPORATION
              NOTES TO CONSOLIDATED CONDENSED FINANCIAL STATEMENTS
          (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS) (UNAUDITED)

  F. - FINANCING


  On January 26, 1999, STERIS entered into a $400,000 Credit Facility. The
  Credit Facility includes an unsecured revolver of $250,000 which expires
  January 26, 2002. The remaining $150,000 is an unsecured 364 day facility
  originally expiring on January 25, 2000, which has been extended and will
  expire on January 23, 2001, subject to being further extended at maturity for
  an additional 364 days. The $400,000 Credit Facility may be used for general
  corporate purposes and will bear interest at either KeyBank National
  Association's prime rate or at LIBOR plus a margin. The Credit Facility
  contains customary covenants which include maintenance of certain financial
  ratios. At December 31, 1999, the outstanding borrowings under the existing
  Credit Facility were $260,000.


  The Company has now repurchased 3.7 million Common Shares as a part of its
  previously announced open market buy-back program. No Common Shares were
  repurchased in the latest quarter.

  G. - CONTINGENCIES

  There are various pending lawsuits and claims arising out of the conduct of
  STERIS's business. In the opinion of management, the ultimate outcome of these
  lawsuits and claims will not have a material adverse effect on STERIS's
  consolidated financial position or results of operations. STERIS believes it
  presently maintains a prudent amount of product liability insurance coverage
  and associated deductible levels.

  On December 15, 1999, STERIS Corporation received a warning letter from the
  Food and Drug Administration ("FDA") in connection with the FDA's recent
  inspection of STERIS's manufacturing facility in Mentor, Ohio. Since the
  inspection and receipt of the warning letter, STERIS has been working
  diligently with the FDA to resolve the FDA's concerns and will continue to
  cooperate with the FDA to reach a final resolution of all concerns. Although
  no assurance can be given as to the timing of any such resolution, management
  believes this matter will not have a material adverse effect on STERIS's
  financial condition, results of operations, or cash flows.

  H. - ACQUISITION

  During the fourth quarter fiscal 2000, the Company purchased a minority equity
  interest in SterilTek, a provider of sterilization management and outsourcing
  services for health care facilities.




                                       7
<PAGE>   8



                     INDEPENDENT ACCOUNTANTS' REVIEW REPORT

  Board of Directors and Shareholders
  STERIS Corporation

  We have reviewed the accompanying consolidated condensed balance sheet of
  STERIS Corporation and subsidiaries as of December 31, 1999, and the related
  consolidated condensed statements of income for the three-month and nine-month
  periods ended December 31, 1999 and 1998, and the consolidated condensed
  statements of cash flows for the nine-month periods ended December 31, 1999
  and 1998. These financial statements are the responsibility of the Company's
  management.

  We conducted our review in accordance with standards established by the
  American Institute of Certified Public Accountants. A review of interim
  financial information consists principally of applying analytical procedures
  to financial data, and making inquiries of persons responsible for financial
  and accounting matters. It is substantially less in scope than an audit
  conducted in accordance with auditing standards generally accepted in the
  United States, which will be performed for the full year with the objective of
  expressing an opinion regarding the financial statements taken as a whole.
  Accordingly we do not express such an opinion.

  Based upon our reviews, we are not aware of any material modifications that
  should be made to the accompanying consolidated condensed financial statements
  referred to above for them to be in conformity with accounting principles
  generally accepted in the United States.

  We have previously audited, in accordance with auditing standards generally
  accepted in the United States, the consolidated balance sheet of STERIS
  Corporation and subsidiaries as of March 31, 1999 and the related consolidated
  statements of operations, shareholders' equity and cash flows for the year
  then ended, not presented herein, and in our report dated April 26, 1999, we
  expressed an unqualified opinion on those consolidated financial statements.
  In our opinion, the information set forth in the accompanying consolidated
  condensed balance sheet as of March 31, 1999, is fairly stated, in all
  material respects, in relation to the consolidated balance sheet from which it
  is derived.

                                                     Ernst & Young LLP

  Cleveland, Ohio
  January 24, 2000


                                       8
<PAGE>   9



  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
  RESULTS OF OPERATIONS



  RESULTS OF OPERATIONS
  ---------------------

  Net revenue decreased by 5.2% to $195.1 million in the third quarter fiscal
  2000 from $205.8 million in the third quarter fiscal 1999. The decline in
  revenues appeared to be largely attributable to delays in capital equipment
  purchases because of concerns over Y2K, the Balanced Budget Act of 1997 which
  reduced Medicare reimbursements and caused many hospitals to slow capital
  purchases, and the recent and pending global consolidations of companies in
  the biopharmaceutical industry. Net revenue decreased to $570.5 million in the
  first nine months of fiscal 2000 from $570.7 million in the same period in
  fiscal 1999. Health Care Group revenues in the fiscal third quarter decreased
  3.5% from the prior year period to $145.2 million, or 74.4% of total Company
  revenues. Scientific and Industrial Group revenues were $49.9 million in the
  third quarter, a decrease of 9.8% from the prior year period. Health Care
  Group revenues in the first nine months of fiscal 2000 increased from the
  prior year period to $424.4 million, or 74.4% of total Company revenues.
  Scientific and Industrial Group revenues were $146.1 million in the first nine
  months of fiscal 2000, a decrease of 0.2% from the prior year period. Revenues
  from consumable products, accessories, and services were 58.8% of net revenue
  for the quarter.

  The costs of products and services sold decreased by 1.1% to $108.0 million in
  the third quarter fiscal 2000 from $109.3 million in the third quarter fiscal
  1999. The costs of products and services sold increased by 2.5% to $310.8
  million for the first nine months of fiscal 2000 from $303.3 million for the
  first nine months of fiscal 1999. The cost of products and services sold as a
  percentage of net revenue was 55.4% for the third quarter fiscal 2000 compared
  to 53.1% for the same period in fiscal 1999. The increase in the cost of
  products and services sold as a percentage of net revenue reflects the impact
  of lower capital equipment sales for the period upon the absorption of fixed
  overhead. The Company has engaged an outside firm to assist with a focused
  project aimed at improving the efficiency and profitability of its major
  manufacturing operations.

  Selling, informational, and administrative expenses increased by 22.7% to
  $61.1 million in the third quarter fiscal 2000 from $49.8 million in the third
  quarter fiscal 1999. Selling, informational, and administrative expenses
  increased by 18.2% to $177.3 million in the first nine months of fiscal 2000
  from $150.0 million in the first nine months of fiscal 1999. The increase in
  expenses during the quarter reflected higher payroll and marketing costs
  primarily incurred to support the expansion and reorientation of the U.S.
  Health Care field organization, the addition of a production facility which
  was acquired as a result of a business combination, as well as a higher level
  of depreciation expense than the prior year. The expenses as a percentage of
  net revenue increased to 31.3% in the third quarter fiscal 2000 from 24.2% in
  the third quarter fiscal 1999.

  Research and development expenses decreased by 6.5% to $5.8 million in the
  third quarter fiscal 2000 from $6.2 million in the third quarter fiscal 1999.
  Research and development expenses decreased by 3.3% to $17.7 million in the
  first nine months fiscal 2000 from $18.3 million in the first nine months
  fiscal 1999 as a result of continued consolidation and rationalization of the
  research and development activities of acquired businesses.

  Interest expense increased by 32.3% to $4.1 million in the third quarter
  fiscal 2000 from $3.1 million in the third quarter fiscal 1999. Interest
  expense increased by 47.4% to $11.5 million in the first nine months fiscal
  2000 from $7.8 million in the first nine months fiscal 1999. The increase was
  due to the additional borrowing under the Credit Facility principally for
  purchases of property, plant, and equipment, acquisition of businesses, and
  repurchase of Common Shares.


                                       9
<PAGE>   10



  Net income for the third quarter of fiscal 2000 decreased by 52.6% to $10.9
  million ($.16 per share) from $23.0 million ($.33 per share) in the same
  period in fiscal 1999. Net income for the first nine months of fiscal 2000
  decreased by 38.2% to $34.7 million ($.51 per share) from $56.1 million ($.79
  per share) in the same period in fiscal 1999.

  LIQUIDITY AND CAPITAL RESOURCES
  -------------------------------

  The Company had $28.6 million in cash and cash equivalents as of December 31,
  1999, compared to $23.7 million of the same at March 31, 1999. The increase
  was primarily attributable to cash received from operating activities and
  borrowings, offset by purchases of property, plant, and equipment, acquisition
  of businesses, and repurchase of Common Shares.

  Accounts receivable decreased by 2.6% to $224.4 million as of December 31,
  1999, compared to $230.3 million at March 31, 1999. The decrease reflected
  seasonal changes in revenues and increased collections.

  Inventory increased by 31.1% to $130.2 million as of December 31, 1999,
  compared to $99.3 million at March 31, 1999. The increase in inventories
  during the period was due to an increase in costs to support product sales and
  anticipated future product sales.

  Prepaid expenses and other assets decreased by 0.6% to $18.1 million as of
  December 31, 1999, compared to $18.2 million at March 31, 1999.

  Property, plant, and equipment increased by 13.4% to $422.3 million as of
  December 31, 1999, compared to $372.4 million at March 31, 1999. The increase
  was due to investments in manufacturing equipment, informational technology
  systems, and contract services operations.

  Intangibles increased by 0.9% to $283.3 million as of December 31, 1999,
  compared to $280.8 million at March 31, 1999.

  Current liabilities decreased by 4.0% to $150.9 million as of December 31,
  1999, compared to $157.1 million at March 31, 1999. The decrease resulted from
  reductions in the current portion of long-term indebtedness and accrued
  expenses.

  Long-term indebtedness increased by 20.1% to $265.9 million as of December 31,
  1999, compared to $221.5 million at March 31, 1999. The increase was due
  primarily to fund purchases of property, plant, and equipment, business
  acquisitions, and the repurchase of Common Shares.

  Other long-term liabilities increased by 0.8% to $49.0 million as of December
  31, 1999, compared to $48.6 million at March 31, 1999.

  On January 26, 1999, STERIS entered into a $400 million Credit Facility. The
  Credit Facility includes an unsecured revolver of $250 million which expires
  January 26, 2002. The remaining $150 million is an unsecured 364 day facility
  originally expiring on January 25, 2000, which has been extended and will
  expire on January 23, 2001, subject to being further extended at maturity for
  an additional 364 days. The $400 million Credit Facility may be used for
  general corporate purposes and will bear interest at either KeyBank National
  Association's prime rate or at LIBOR plus a margin. The Credit Facility
  contains customary covenants which include maintenance of certain financial
  ratios. At December 31, 1999, the outstanding borrowings under the existing
  Credit Facility were $260 million.


                                       10
<PAGE>   11



  The Company has no material commitments for capital expenditures. The Company
  believes that its cash requirements will increase due to increased sales
  requiring more working capital, accelerated research and development, and
  potential acquisitions or investments in complementary businesses. However,
  the Company believes that its available cash, cash flow from operations, and
  sources of credit will be adequate to satisfy its capital needs for the
  foreseeable future.

  CONTINGENCIES
  -------------

  For a discussion of contingencies, see Note G to the consolidated condensed
  financial statements.

  SEASONALITY
  -----------

  Historical data indicates that financial results were subject to recurring
  seasonal fluctuations. A number of factors have contributed to the seasonal
  patterns, including sales promotion and compensation programs, Customer buying
  patterns of capital equipment, and international business practices. Sales and
  profitability of certain of the acquired and consolidated product lines have
  historically been disproportionately weighted toward the latter part of each
  quarter and each fiscal year. Various changes in business practices resulting
  from the integration of acquired businesses into STERIS may alter the
  historical patterns of the previously independent businesses.

  YEAR 2000 DATE CONVERSION
  -------------------------

  An issue affecting many companies is how computer applications process
  date-sensitive information. Some older computer programs were written using
  two digits rather than four to define the applicable year. As a result, those
  computer programs have time-sensitive software that recognize a date using
  "00" as the year 1900 rather than the year 2000. Without corrective actions,
  this could cause disruptions of operations.

  The Company completed all Year 2000 readiness work and has experienced no
  significant problems. The Y2K concerns that might have impacted Customer
  buying decisions have been addressed above.

  Operating expenses include costs incurred in preparing systems and
  applications for the year 2000. The Company incurred internal staff costs as
  well as outside services and other expenses related to the conversion and
  testing of the systems and applications. These costs were immaterial.

  EURO
  ----

  On January 1, 1999, eleven of the fifteen member countries of the European
  Monetary Union (EMU) began a three-year transition phase during which a common
  currency called the Euro was adopted as their legal currency. The Euro began
  trading on currency exchanges and is available for non-cash transactions.
  During the transition period, parties may pay for goods and services using
  either the Euro or the participating country's legacy currency on a "no
  compulsion, no prohibition" basis. The conversion rates between the existing
  legacy currencies and the Euro were fixed on January 1, 1999. The legacy
  currencies will remain legal tender for cash transactions between January 1,
  1999, and January 1, 2002, at which time all legacy currencies will be
  withdrawn from circulation and the new Euro denominated bills and coins will
  be used for cash transactions.

  The Company has several operations within the eleven participating countries
  that are using the Euro as their local currency. Additionally, the Company's
  operations in other European countries and elsewhere in the world will be
  conducting business transactions with Customers and suppliers that will be
  denominated in the Euro. Euro denominated bank accounts have been established
  to accommodate Euro transactions.

  The Company has established plans to review strategic and tactical issues
  arising from the Euro conversion. Over the past several periods, these plans
  have focused on aspects of the Euro conversion that required adjustment or
  compliance by January 1, 1999, and for conducting Euro-denominated business.
  These aspects included transacting business in the Euro, the competitive
  impact on product pricing, and adjustments to billing systems to handle
  parallel currencies. The Company has determined that these systems have the
  capability to handle Euro transactions and are currently in a position to
  transact business in Euros. Continuing analysis and development efforts will
  help ensure that the implementation of the Euro meets the timetable and
  regulations established by the EMU.


                                       11
<PAGE>   12


  Based on current estimates, the Company does not expect the costs incurred to
  address the Euro will have a material impact on its financial condition,
  results of operations, or cash flows.

  FORWARD-LOOKING INFORMATION
  ---------------------------

  This Form 10-Q contains statements concerning certain trends and other
  forward-looking information affecting or relating to the Company and its
  industry that are intended to qualify for the protections afforded
  "forward-looking statements" under the Private Securities Litigation Reform
  Act of 1995. Forward-looking statements may be identified by the use of
  forward-looking terms such as "may," "will," "expects," "anticipates,"
  "plans," "estimates," "projects," "targets," "forecasts," or "seeks" or the
  negative of such terms or other variations on such terms or comparable
  terminology. There are many important factors that could cause actual results
  to differ materially from those in the forward-looking statements. Many of
  these important factors are outside STERIS's control. Changes in market
  conditions, including competitive factors and changes in government
  regulations, could cause actual results to differ materially from the
  Company's expectations. No assurance can be provided as to any future
  financial results. Other potentially negative factors that could cause actual
  results to differ materially from those in the forward-looking statements
  include (a) the possibility that the continuing integration of acquired
  businesses will take longer than anticipated, (b) the potential for increased
  pressure on pricing that leads to erosion in profit margins, (c) the
  possibility that market demand will not develop for new technologies,
  products, and applications or that regulatory actions may affect market
  demand, (d) the potential effects of fluctuations in foreign currencies where
  the Company does a sizable amount of business, (e) the possibility that the
  Company's activities related to changes in its sales force will take longer or
  incur greater expense than anticipated and (f) the possibility of reduced
  demand, or reductions in the rate of growth in demand, for the Company's
  products and services.

  QUANTITATIVE AND QUALITATIVE DISCLOSURE ABOUT MARKET RISK
  ---------------------------------------------------------

  A discussion of market risk exposures is included in Part II, Item 7a,
  "Quantitative and Qualitative Disclosure about Market Risk," of the Company's
  1999 Annual Report and Form 10- K. There were no material changes during the
  nine months ended December 31, 1999.



  PART II      OTHER INFORMATION



  ITEM 1                    LEGAL PROCEEDINGS
  ------                    -----------------

  Reference is made to Part I, Item 1., Note G of this Report on Form 10-Q,
  which is incorporated herein by reference.




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<PAGE>   13



  ITEM 6               EXHIBITS AND REPORTS ON FORM 8-K
  ------               --------------------------------

  (a)                  Exhibits
                       --------

<TABLE>
<CAPTION>
       EXHIBIT NUMBER         EXHIBIT DESCRIPTION
       --------------         -------------------
<S>                           <C>
             10.1             First Amendment Agreement, dated January 25, 2000,
                              among STERIS Corporation, various financial
                              institutions and KeyBank National Association, as
                              Agent.
             10.2             Assignment and Acceptance Agreement, dated January 24, 2000,
                              between The Bank of New York ("Assignor") and KeyBank National
                              Association ("Assignee").
             10.3             Tranche B Note, dated January 24, 2000, between
                              STERIS Corporation and KeyBank National
                              Association.
             15.1             Letter Re: Unaudited Interim Financial Information
             27.1             Financial Data Schedule
</TABLE>


   (b)                 Reports on Form 8-K
                       -------------------

   None



                                    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.




                                                 STERIS Corporation

                                                 (Registrant)



                                                 /s/ Les C. Vinney
                                                 -----------------

                                                 Les C. Vinney
                                                 Senior Vice President and
                                                 Chief Financial Officer
                                                 (Principal Financial Officer)
                                                 February 11, 2000




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