<PAGE>   1

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                                 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 SEPTEMBER 30, 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 September 30, 1999: 67,497,700


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<PAGE>   2



PART I         FINANCIAL INFORMATION


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

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

<TABLE>
<CAPTION>
                                                                            SEPTEMBER 30,        MARCH 31,
                                                                                1999               1999
                                                                            --------------     -------------
<S>                                                                            <C>               <C>
ASSETS
Current assets:
  Cash and cash equivalents                                                    $  32,310         $  23,680
  Accounts receivable                                                            219,389           230,346
  Inventories                                                                    124,597            99,279
  Current portion of deferred income taxes                                        21,910            21,910
  Prepaid expenses and other assets                                               16,770            18,182
                                                                               ---------         ---------
TOTAL CURRENT ASSETS                                                             414,976           393,397
Property, plant, and equipment                                                   408,037           372,386
Accumulated depreciation                                                        (127,698)         (111,105)
                                                                               ---------         ---------
  Net property, plant, and equipment                                             280,339           261,281
Intangibles                                                                      282,634           280,750
Accumulated amortization                                                         (75,933)          (72,499)
                                                                               ---------         ---------
  Net intangibles                                                                206,701           208,251
Other assets                                                                       3,400             3,067
                                                                               ---------         ---------
TOTAL ASSETS                                                                   $ 905,416         $ 865,996
                                                                               =========         =========

LIABILITIES AND SHAREHOLDERS' EQUITY
  Current liabilities:
  Current portion of long-term indebtedness                                    $   1,816         $   2,200
  Accounts payable                                                                39,739            47,431
  Accrued expenses and other                                                     104,669           107,506
                                                                               ---------         ---------
TOTAL CURRENT LIABILITIES                                                        146,224           157,137
Long-term indebtedness                                                           266,450           221,500
Deferred income taxes                                                              2,810             2,810
Other long-term liabilities                                                       48,845            48,612
                                                                               ---------         ---------
TOTAL LIABILITIES                                                                464,329           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 67,498 at September 30, 1999, and 67,956 at
  March 31, 1999, excluding 1,081 and 523 treasury shares, respectively          204,304           222,946
Retained earnings                                                                243,606           219,863
Cumulative translation adjustment                                                 (6,823)           (6,872)
                                                                               ---------         ---------
TOTAL SHAREHOLDERS' EQUITY                                                       441,087           435,937
                                                                               ---------         ---------
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY                                     $ 905,416         $ 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                   SIX MONTHS ENDED
                                                            SEPTEMBER 30                        SEPTEMBER 30
                                                    ---------------------------------------------------------------
                                                       1999             1998               1999             1998
                                                    ---------         ---------         ---------         ---------

<S>                                                 <C>               <C>               <C>               <C>
Net revenues                                        $ 198,602         $ 191,125         $ 375,415         $ 364,900
Cost of goods and services sold                       108,001           101,621           202,802           194,082
                                                    ---------         ---------         ---------         ---------
Gross profit                                           90,601            89,504           172,613           170,818

Costs and expenses:
  Selling, informational, and administrative           58,634            50,693           116,285           100,224
  Research and development                              5,715             6,074            11,923            12,103
                                                    ---------         ---------         ---------         ---------
                                                       64,349            56,767           128,208           112,327
                                                    ---------         ---------         ---------         ---------

Income from operations                                 26,252            32,737            44,405            58,491
Interest expense                                       (3,903)           (2,325)           (7,396)           (4,719)
Interest income and other                                 852               360             1,248               515
                                                    ---------         ---------         ---------         ---------
Income before income taxes                             23,201            30,772            38,257            54,287
Income tax expense                                      8,793            12,001            14,514            21,171
                                                    ---------         ---------         ---------         ---------
Net income                                          $  14,408         $  18,771         $  23,743         $  33,116
                                                    =========         =========         =========         =========

Net income per share - basic                        $    0.21         $    0.27         $    0.35         $    0.49
                                                    =========         =========         =========         =========
Net income per share - diluted                      $    0.21         $    0.27         $    0.35         $    0.47
                                                    =========         =========         =========         =========
</TABLE>

            See notes to consolidated condensed financial statements.



                                       3
<PAGE>   4


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

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

<TABLE>
<CAPTION>
                                                                        SIX MONTHS ENDED
                                                                          SEPTEMBER 30
                                                                 ------------------------------
                                                                      1999             1998
                                                                 --------------  --------------
<S>                                                                 <C>              <C>
OPERATING ACTIVITIES
Net income                                                          $ 23,743         $ 33,116
Adjustments to reconcile net income to
   net cash (used in) provided by operating activities:
   Depreciation and amortization                                      20,027           15,225
   Deferred income taxes                                                   0           (7,761)
   Other items                                                          (403)          (1,776)
   Changes in operating assets and liabilities:
       Accounts receivable                                            11,521           12,037
       Inventories                                                   (25,318)         (20,329)
       Other assets                                                    5,872           (2,135)
       Accounts payable and accruals                                 (10,861)          (1,533)
                                                                    --------         --------
NET CASH PROVIDED BY OPERATING ACTIVITIES                             24,581           26,844

INVESTING ACTIVITIES
Purchases of property, plant, equipment, and patents                 (33,524)         (31,458)
Investment in businesses                                              (6,259)         (39,992)
                                                                    --------         --------
NET CASH USED IN INVESTING ACTIVITIES                                (39,783)         (71,450)

FINANCING ACTIVITIES
Payments on long-term obligations                                     (1,134)            (589)
Borrowing under credit facility                                       45,000           50,000
Purchase of treasury shares                                          (28,712)          (2,495)
Stock option and other equity transactions                             8,241            5,594
                                                                    --------         --------
NET CASH PROVIDED BY FINANCING ACTIVITIES                             23,395           52,510
Effect of exchange rate changes on cash and cash equivalents             437                1
                                                                    --------         --------
INCREASE IN CASH AND CASH EQUIVALENTS                                  8,630            7,905
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                      23,680           17,172
                                                                    ========         ========
CASH AND CASH EQUIVALENTS AT END OF PERIOD                          $ 32,310         $ 25,077
                                                                    ========         ========
</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 SEPTEMBER 30, 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 healthcare,
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                  SIX MONTHS ENDED
                                                           SEPTEMBER 30                       SEPTEMBER 30
                                                 ---------------------------------  ---------------------------------
                                                     1999               1998            1999               1998
                                                 --------------    ---------------  --------------     --------------
<S>                                                     <C>                <C>             <C>                <C>
  Weighted average Common
  Shares outstanding - basic                            67,455             68,326          67,478             68,222

  Dilutive effect of stock options                       1,020              2,429           1,288              2,496
                                                 --------------    ---------------  -------------- --- --------------
  Weighted average Common Shares and
  equivalents - diluted                                 68,475             70,755          68,766             70,718
                                                 ==============    ===============  ==============     ==============
</TABLE>

D. - COMPREHENSIVE INCOME

Comprehensive income amounted to $14,879 and $19,434, net of tax, for the
quarters ended September 30, 1999 and 1998, respectively. Comprehensive income
amounted to $23,792 and $33,117, net of tax, for the six months ended September
30, 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>
                                                                   SEPTEMBER 30,               MARCH 31,
                                                                        1999                      1999
                                                                ---------------------     ---------------------
<S>                                                                          <C>                       <C>
  Raw material                                                               $46,132                   $36,878
  Work in process                                                             24,406                    19,585
  Finished goods                                                              54,059                    42,816
                                                                ---------------------     ---------------------
                                                                            $124,597                   $99,279
                                                                =====================     =====================
</TABLE>

The increase in inventories during the period was due to an increase in costs to
support product sales and anticipated future product sales.


                                       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 expiring on
January 25, 2000, which can be extended annually for 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 September 30, 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.

H. - ACQUISITIONS

Early in the second quarter fiscal 2000, the Company acquired the assets of
Quality Sterilization Systems (QSS), a contract sterilization business located
near Minneapolis, Minnesota. QSS primarily provides contract sterilization
services for medical device manufacturers in the upper Midwest. Also, during the
second quarter fiscal 2000, the Company completed the acquisition of privately
held FoodLabs, Inc. FoodLabs, Inc., located in Manhattan, Kansas, provides
analytical, product development, and consulting services to the food and
agricultural industries, with a particular focus on food safety. These
acquisitions have been accounted for as purchase transactions.



                                       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 September 30, 1999, and the related
consolidated condensed statements of income for the three-month and six-month
periods ended September 30, 1999 and 1998, and the consolidated condensed
statements of cash flows for the six-month periods ended September 30, 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 generally accepted auditing standards, 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 generally accepted
accounting principles.

We have previously audited, in accordance with generally accepted auditing
standards, 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
October 27, 1999



                                       8
<PAGE>   9


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

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

Net revenue increased by 3.9% to $198.6 million in the second quarter fiscal
2000 from $191.1 million in the second quarter fiscal 1999. Net revenue
increased by 2.9% to $375.4 million in the first six months of fiscal 2000 from
$364.9 million in the same period in fiscal 1999. Health Care Group revenues in
the fiscal second quarter increased 3.5% from the prior year period to $148.1
million, or 74.6% of total Company revenues. Scientific and Industrial Group
revenues were $50.5 million in the second quarter, an increase of 5.1% from the
prior year period. Health Care Group revenues in the first six months of fiscal
2000 increased 2.0% from the prior year period to $279.3 million, or 74.4% of
total Company revenues. Scientific and Industrial Group revenues were $96.1
million in the first six months of fiscal 2000, an increase of 5.6% from the
prior year period. Revenues from consumables and services were 56.7% of sales
for the quarter, up from 53.5% in last year's second quarter.

The costs of products and services sold increased by 6.3% to $108.0 million in
the second quarter fiscal 2000 from $101.6 million in the second quarter fiscal
1999. The costs of products and services sold increased by 4.5% to $202.8
million for the first six months of fiscal 2000 from $194.1 million for the
first six months of fiscal 1999. The cost of products and services sold as a
percentage of net revenue was 54.4% for the second quarter fiscal 2000 compared
to 53.2% for the same period in fiscal 1999. The increase in the cost of
products and services sold as a percentage of net revenue reflects a change in
the classification of certain service costs previously treated as general
operating expenses. The change reduced gross margin by approximately 0.7% in the
second quarter and 0.6% in the first half.

Selling, informational, and administrative expenses increased by 15.7% to $58.6
million in the second quarter fiscal 2000 from $50.7 million in the second
quarter fiscal 1999. Selling, informational, and administrative expenses
increased by 16.0% to $116.3 million in the first six months of fiscal 2000 from
$100.2 million in the first six months of fiscal 1999. The increase in expenses
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 production facilities which were acquired as a result of business
combinations, as well as the costs related to the termination of the proposed
acquisition of Isotron plc, which resulted in a charge of $0.5 million in the
second quarter. The expenses as a percentage of net revenue increased to 29.5%
in the second quarter fiscal 2000 from 26.5% in the second quarter fiscal 1999.

Research and development expenses decreased by 5.9% to $5.7 million in the
second quarter fiscal 2000 from $6.1 million in the second quarter fiscal 1999.
Research and development expenses decreased by 1.5% to $11.9 million in the
first six months fiscal 2000 from $12.1 million in the first six months fiscal
1999.

Interest expense increased by 67.9% to $3.9 million in the second quarter fiscal
2000 from $2.3 million in the second quarter fiscal 1999. Interest expense
increased by 56.7% to $7.4 million in the first six months fiscal 2000 from $4.7
million in the first six months fiscal 1999. The increase


                                       9
<PAGE>   10


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.

Net income for the second quarter of fiscal 2000 decreased by 23.2% to $14.4
million ($.21 per share) from $18.8 million ($.27 per share) in the same period
fiscal 1999. Net income for the first six months of fiscal 2000 decreased by
28.3% to $23.7 million ($.35 per share) from $33.1 million ($.47 per share) in
the same period fiscal 1999.

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

The Company had $32.3 million in cash and cash equivalents as of September 30,
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 4.8% to $219.4 million as of September 30,
1999, compared to $230.3 million at March 31, 1999. The decrease reflected
seasonal changes in revenues and increased collections.

Inventory increased by 25.5% to $124.6 million as of September 30, 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 7.8% to $16.8 million as of
September 30, 1999, compared to $18.2 million at March 31, 1999.

Property, plant, and equipment increased by 9.6% to $408.0 million as of
September 30, 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 0.7% to $282.6 million as of September 30, 1999,
compared to $280.8 million at March 31, 1999.

Current liabilities decreased by 7.0% to $146.2 as of September 30, 1999,
compared to $157.1 million at March 31, 1999.

Long-term indebtedness increased by 20.3% to $266.5 million as of September 30,
1999, compared to $221.5 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 0.5% to $48.8 million as of September
30, 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
expiring on January 25, 2000, which can be extended annually for 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 September 30, 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 STERIS and most other companies is how computer systems and
applications recognize and 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 a system failure or
miscalculations causing disruptions of operations, including, among other
things, a temporary inability to process transactions, send invoices, or engage
in similar normal business activities.

The Company has investigated the impact of the year 2000 issue on its products
and does not anticipate any effect on the performance of its products. The
Company is in the process of assessing and implementing necessary changes for
all areas of the Company's business which could be impacted; these include such
areas as business computer systems, technical infrastructure, plant floor
equipment, building infrastructure, end-user computing, and suppliers. The
Company has initiated a project to prepare its computer systems for the year
2000 and is addressing the year 2000 issues.

The Company's year 2000 program activities include the identification of
affected hardware and software, the development of a plan for remediating those
systems in the most effective manner, the execution of that plan, which includes
continuous testing, and the monitoring of the program's success. Although
various locations are at differing stages of readiness with respect to the
various focus areas, the identification and plan development phases of the
project are completed. The Company has substantially completed the program, and
continuous review and testing are being conducted to help ensure that compliance
is achieved and maintained as the year 2000 approaches.


                                       11
<PAGE>   12


The Company has implemented year 2000 compliant systems in a number of areas,
including order entry systems. In a number of instances, the Company has
replaced non-compliant systems with newer systems which will significantly
improve functionality as well as appropriately interpret the calendar year 2000
and beyond. Although the timing of these actions may have been influenced by the
year 2000 issue, in virtually all instances they involved capital expenditures
that would have occurred in the normal course of business. While the Company is
implementing a year 2000 vendor compliance program, the Company has little
direct control over whether its suppliers will make the appropriate
modifications to their systems and applications on a timely basis.

As part of the year 2000 program, contingency plans are being formalized as the
target date for completion approaches. Business disruption scenarios have been
identified and continue to be reviewed and appropriate strategies are being
evaluated in the development of these various plans. The Company continues to
develop contingency plans (e.g., the selection of alternative suppliers) to
address the potential business disruption scenarios that are being identified.

Operating expenses include costs incurred in preparing systems and applications
for the year 2000. The Company expects to incur internal staff costs as well as
outside services (including consultants) and other expenses related to the
conversion and testing of the systems and applications. These costs, which are
expensed as incurred, have been immaterial to date. The year 2000 costs include
internal modification and testing costs as well as costs associated with supply
chain risk assessment and contingency planning.

Based on assessments completed to date and compliance plans in process, the
Company believes that it has an effective program in place to resolve the year
2000 challenges in a timely manner and the Company does not expect that the year
2000 issues will have a material effect on its business operations or results of
operations. However, satisfactory completion of the program may not prevent
business disruptions resulting from actions of critical suppliers and Customers.
Such disruptions would impair the Company's ability to obtain necessary
materials for production or sell products to Customers. If such disruptions
occurred, the Company may experience lost or delayed sales and profits depending
on the duration of the disruptions. Key aspects of the program are addressing
potential uncertainties but the Company's ability to be fully confident of
conditions related to third parties is limited. Currently, the Company cannot
reasonably estimate the amount of potential lost or delayed sales and profits.

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.



                                       12
<PAGE>   13


The Company has several operations within the eleven participating countries
that will be utilizing the Euro as their local currency in 1999. 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's exposure to changes in foreign
exchange rates may also be reduced as a result of the Euro conversion.

The Company has established plans to review strategic and tactical areas 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 during 1999.
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 is 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.

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 or
results of operations.

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. 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, (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 six
months ended September 30, 1999.


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<PAGE>   14


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.

ITEM 2    CHANGES IN SECURITIES AND USE OF PROCEEDS
------    -----------------------------------------

On July 29, 1999, the Company issued 100,000 Common Shares, without par value,
to the shareholders of FoodLabs, Inc. in exchange for all of the issued and
outstanding capital stock of FoodLabs, Inc. The Company issued its Common Shares
in reliance on the exemption from registration provided by Rule 505 promulgated
under the Securities Act of 1933, as amended (the "1933 Act"). The offering of
the Common Shares satisfied the terms and conditions of Rules 501 and 502 under
the 1933 Act, and the Common Shares had an aggregate offering price not
exceeding $5 million and were issued to 35 or fewer purchasers.

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

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

  EXHIBIT NUMBER       EXHIBIT DESCRIPTION
  --------------       -------------------

      15.1             Letter Re: Unaudited Interim Financial Information

      27.1             Financial Data Schedule

(b)                    Reports on Form 8-K

Current report on form 8-K, filed August 31, 1999, in connection with the
announcement by the Company that it had allowed its recommended cash offer to
purchase Isotron plc to lapse.



                                       14
<PAGE>   15


                                    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)
                                             November 12, 1999




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