<PAGE>
 
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                      SECURITIES AND EXCHANGE COMMISSION
                           WASHINGTON, D. C.  20549

                                   FORM 10-K

                 Annual Report Pursuant to Section 13 or 15(d)
                    of the Securities Exchange Act of 1934
                                        
                  For the fiscal year ended December 31, 1998
                         Commission File Number 1-9983
                                        

                           OEC MEDICAL SYSTEMS, INC.
            (Exact name of registrant as specified in its charter)


                Delaware                                 94-2538512
    (State or other jurisdiction of                   (I.R.S. Employer 
     incorporation or organization)                 Identification Number)
                                    
       384 Wright Brothers Drive                          84116 
          Salt Lake City, Utah                          (Zip Code) 
(Address of principal executive offices)
 
 
                                (801) 328-9300
                        (Registrant's telephone number)

          Securities registered pursuant to Section 12(b) of the Act:
                  Listed on the New York Stock Exchange (NYSE)

                          Common Stock, $.01 par value

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

  Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months or for such short period that the Registrant
was required such reports and (2) has been subject to such filing requirements
for the past 90 days.

Yes X    No  
    ---    ---

  Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [  ]

  The aggregate market value of Common Stock held by non-affiliates (based on
the closing sales price on the New York Stock Exchange) on March 1, 1999 was
approximately $326,331,501.

  As of March 1, 1999, there were 12,753,477 shares of Common Stock with $.01
par value outstanding.

Documents Incorporated by Reference:                    Form 10-K Part

(1)  Portions of Definitive Proxy Statement to be mailed to stockholders in
    connection with the Registrant's 1999 Annual Meeting of Stockholders  I, III
(2)  Portions of the Annual Report to Shareholders for fiscal year ended
December 31, 1998                                                             II

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<PAGE>
 
                           OEC MEDICAL SYSTEMS, INC.
                         1998 FORM 10-K ANNUAL REPORT
                               TABLE OF CONTENTS
                                        
 
PART I
Item 1.        Business                                                   2
Item 2.        Properties                                                 5
Item 3.        Legal Proceedings                                          5
Item 4.        Submission of Matters to a Vote of Security Holders        5
                                                                 
                                                                          
PART II                                                                   
Item 5.        Market for Registrant's Common Equity and                  
                Related Stockholder Matters                               6
Item 6.        Selected Financial Data                                    6
Item 7.        Management's Discussion and Analysis of                    
                Financial Condition and Results of Operations             6
Item 7A.       Quantitative and Qualitative Disclosures about             
                Market Risk                                               6
Item 8.        Financial Statements and Supplemental Data                 6
Item 9.        Changes In and Disagreements with Accountants              
                on Accounting and Financial Disclosure                    6
                                                                          
PART III                                                                  
Item 10.       Directors and Executive Officers of Registrant             7
Item 11.       Executive Compensation                                     8
Item 12.       Security Ownership of Certain Beneficial Owners            
                and Management                                            8 
Item 13.       Certain Relationships and Related Transactions             8
                                                                          
PART IV                                                                   
Item 14.       Exhibits, Financial Statement Schedules and                
                Reports on Form 8-K                                       8

                                       1
<PAGE>
 
                          OEC MEDICAL SYSTEMS, INC. 

                         1998 FORM 10-K ANNUAL REPORT
                                        
                                    PART I
                                        
Except for historical information, this discussion contains forward-looking
statements that involve risks and uncertainties that could cause actual results
to differ materially from those projected.  Such risk and uncertainties include:
product demand and market acceptance; the effect of general economic conditions
and foreign currency fluctuations; the impact of competitive products and
pricing; new product development and commercialization; the effect of the
continuing shift in growth from domestic to international healthcare customers,
and the impact of managed care initiatives in the United States and the ability
to increase operating margins on higher sales as further described in the "Risk
Factors" section on page 5 of this Form 10-K.

Item 1.  Business

   General.  OEC Medical Systems, Inc. ("OEC" or the "Company") develops,
manufactures, markets, and services computer-based X-ray fluoroscopic imaging
systems for use in hospitals, outpatient clinics, physicians' offices and
surgery-centers for minimally invasive intraoperative and interventional
procedures.

   OEC was originally established in Indiana in 1942.  In response to surgeons'
need for improved methods to monitor and guide the implantation of various
internal fixation devices, OEC entered the medical X-ray imaging market in 1972.
Diasonics, Inc. ("Diasonics") in October 1983 acquired OEC as a separate
operating subsidiary. The Company was merged into Diasonics in September of
1993.  As part of the restructuring, the other operating businesses of Diasonics
were spun off to shareholders and the Diasonics name was changed to OEC Medical
Systems, Inc.

   Today, OEC is recognized as the pioneer and continuing United States market
leader of intraoperative X-ray imaging systems.  These systems combine
radiographic and fluoroscopic imaging with digital image processing
capabilities. X-rays are passed through the body and either recorded on
radiographic film or passed through an image intensifier system and displayed as
a real-time fluoroscopic image on a video monitor.  Digital image processing of
the fluoroscopic image improves the image quality, contributes to lowering X-ray
dosage and results in reduced costs for a number of applications.

   OEC seeks to provide cost-effective imaging systems directed towards medical
specialties in which minimally invasive techniques are replacing expensive and
more traumatic open surgical procedures. High quality digital fluoroscopy has
become mandatory in many of today's modern operating rooms. Further, minimally
invasive techniques are expanding into many areas of vascular, neurological,
orthopedic, urological, cardiac and general surgery.  OEC's products are
designed to meet the needs of these new procedures.

   Technical leadership, strong customer relationships, a cost-effective product
line and full-line service capabilities have earned OEC recognition as the
United States market leader in the intraoperative X-ray imaging markets which it
addresses.

   OEC believes its international markets represent a significant growth
opportunity and continues to expand its network of international distributors.
Building on its leadership position in the U.S., OEC's focus is to become the
worldwide leader for intraoperative and interventional fluoroscopic imaging.
With this focus in mind, OEC has been investing in the future through research
and development.  The introductions of the Series 9600 Mobile Digital Imaging
System in 1994; the UroView 2600 urology table, the Mini 6600 and Compact and
Series 7600 all introduced in 1995; the 9600 Mobile Cardiac Cath Lab and the
dual mode Mini 6600 introduced in 1997; and finally, the Compact and Series 7700
introduced in 1998 are the results of these investments.

   OEC's expanding presence in international markets is another example of the
Company's investment in the future.  OEC has strengthened its wholly owned
subsidiaries in France, Germany, Italy and Switzerland with additional personnel
and training, and has designed its new products to be more appealing and
acceptable to international customers. OEC has also strengthened its
international network in new markets by establishing new distributors and
strengthening existing distributors throughout the world.  OEC intends to
continue these activities during 1999.

                                       2
<PAGE>
 
   OEC's Products.  The products produced by OEC consist of mobile X-ray imaging
systems as well as fixed-room urological X-ray imaging systems.

   C-arm Products.  In March 1994, OEC introduced the Series 9600 Mobile Digital
   --------------                                                               
Imaging System. This mobile imaging device can be wheeled from operating room to
operating room to provide high quality, real-time fluoroscopic imaging for a
wide variety of surgical and interventional procedures that require X-ray
guidance.
 
   The modular architecture of the system allows the Series 9600 to be tailored
to meet the needs of the surgeon.  For example, the Series 9600 can be equipped
with an expanded surgical package for general surgery and orthopedics. When
equipped with a vascular special procedures module, it can perform complex
subtraction angiography in the operating room, emergency room, or in radiology.
Prices of the Series 9600 Mobile Digital Imaging System range from $100,000 to
$230,000.

   The Series 9600 Mobile Cardiac Cath Lab was introduced in 1997.  This
proprietary version of the Series 9600 offers the same imaging capability found
in many fixed room cath labs with all the convenience and cost effectiveness of
a mobile imaging system.  This system is the basis for the Company's strategic
alliances with device manufacturers associated with minimally invasive cardiac
surgeries.  Surgeons use the Series 9600 Mobile Cardiac Cath Lab to confirm
patency following minimally invasive cardiac procedures.  Prices for the Series
9600 Mobile Cardiac Cath Lab range from $190,000 to $250,000.
 
   In response to changes brought on by managed healthcare, OEC provides three
lower cost digital mobile X-ray imaging machines - the Compact 7700, Series 7700
and the Mini 6600. These smaller, lower cost machines are specifically designed
to address the imaging requirements of outpatient surgery centers as well as
other satellite surgery delivery sites.  The move towards less invasive
surgeries, with accompanying shorter recovery times, is driving the need for
easy to operate, cost effective fluoroscopic imaging systems in all settings of
the healthcare delivery network.

   The Compact 7700 Digital Mobile C-Arm is a cost effective, simple to operate,
full-body imaging system that can be utilized for most routine, less complicated
surgical procedures.  Its compact, one-piece design (no separate monitor cart)
allows for ease of transport, quick positioning and minimal storage
requirements.  Prices of the Compact 7700 range from $75,000 to $95,000. The
Series 7700 has the same functionality as that of the Compact 7700, but it has a
separate workstation. The addition of the workstation allows the Series 7700 to
be upgraded with features and capabilities necessary to perform more complicated
procedures. The price range for the Series 7700 is $80,000 to $110,000.

   The dual mode version of the Mini 6600 Digital Mobile C-Arm was introduced in
1997.  Like its forerunner the Mini 6600, it is a smaller digital fluoroscopic
imaging system that has been specifically designed to provide high quality
images of upper and lower extremities.  Areas of use include hospital operating
rooms and emergency rooms, outpatient surgery centers, specialty physician
offices and veterinary clinics.  Prices of the Mini 6600 range from $45,000 to
$70,000.

   During 1998, 1997 and 1996, the OEC C-arm products represented 85%, 80% and
77% of total product sales, respectively.

   UroView 2600 Digital Imaging System.  Urology is another surgical specialty
   -----------------------------------                                        
requiring intraoperative imaging that has largely moved away from the use of
static X-ray films to monitor and guide procedural progress.  Diagnostic and
interventional urological procedures are often performed in a separate area of
the operating room environment known as the "Cysto Department". Until the late
1980s, these specialized rooms were equipped with a fixed (bolted down)
urological-specific patient positioning table (motorized in movement) that also
had static X-ray filming capability built in.  These films, once exposed, would
need to be taken to a darkroom in radiology to be developed prior to being
brought back to the Cysto Department for evaluation by the urologist.  This
resulted in long procedural delays.  Additionally, real-time events could not be
recorded since radiographic film produces only  a  static image.  Eventually,
real-time fluoroscopic imaging capabilities were added to these systems.  In
1987, OEC introduced the UroView, which was the industry's first urological
table with fully integrated digital fluoroscopy.  This resulted in significant
image improvement, pulsed fluoroscopy for lower dose than prior systems, and
reduced costs compared to existing urological imaging systems.   Prices for the
UroView system presently range from $210,000 to $230,000.

                                       3
<PAGE>
 
   During 1998, 1997 and 1996, the OEC urology product represented 15%, 20% and
23% of total product sales, respectively.

   Quality. In June 1994, the Company's Quality Assurance System received the
Certificate of Compliance with ISO 9001, the international standard for quality
assurance in design, development, production, installation and servicing.
 
   Sales and Service.  Domestic sales are made primarily through direct
representatives and exclusive independent distributors, with installation and
service performed by OEC.  Most of these distributors have represented OEC
products over many years.

   In Europe, OEC distributes its products primarily through wholly owned
subsidiaries in Italy, France, Germany and Switzerland.  For the rest of the
world, distribution is accomplished through independent dealers and
distributors.
 
   OEC generally warrants its products for twelve months from the date of
installation.  OEC offers service contracts for products for which the warranty
has expired.

   During 1998, 1997 and 1996, service revenue represented 12%, 11% and 13% of
net sales, respectively.
 
   Manufacturing.  OEC's manufacturing operations are located in Salt Lake City,
Utah; Warsaw, Indiana, and Wendelstein, Germany.  The Salt Lake City facility
has just been expanded by 40,000 square feet to accommodate increased product
demand and future anticipated growth. The Warsaw, Indiana facility manufacturers
the sheet metal enclosures, the mechanical C-arm assembly and all major
mechanical components for OEC's products.  The electronics and imaging
components for the Mini 6600, Series 9600, and Uroview 2600 are assembled at
OEC's Salt Lake City facility, which also performs final assembly and test of
the finished devices. The Wendelstein, Germany facility manufactures the Compact
7700 and the Series 7700.

   Competition.  The market for mobile X-ray imaging and fixed urological
imaging products is highly competitive.  Many of OEC's existing and potential
competitors have substantially greater financial, marketing and technological
resources than OEC.  In the market for products similar to OEC's Series 9600
Mobile C-arm, OEC competes with General Electric, Siemens Medical Systems, Inc.,
Philips Medical Systems, Inc. and Toshiba Medical Systems, Inc.  Competitive
companies offering products similar to the Mini 6600 include Hologic, Inc., and
Lunar Corporation.  The Compact 7700 and Series 7700 compete with similar
products from International Medical Systems, Inc.  Competitive companies
offering products similar to the Uroview 2600 include Shimadzu, Picker
International, Inc., Dornier Medical Systems, Inc. and Liebel-Flarsheim Company.
OEC competes on the basis of price, imaging quality, technological innovation,
upgradeability, reliability and the quality of service and support.

   Backlog.  At December 31, 1998, OEC's backlog was approximately $39.5
million, as compared with approximately $32.3 million at December 31, 1997.  OEC
includes in backlog only firm orders deliverable within 12 months.  Backlog also
includes service contract revenue, which will be earned over the next twelve
months.

   Research and Development.  The medical imaging business involves rapid
technological change and innovation.  OEC believes that its ability to use
technological innovation to advance the clinical utility of diagnostic imaging
has been and will continue to be a significant factor in its success.  OEC has
continued to invest in research and development to identify solutions to the
imaging requirements in the area of minimally invasive medical procedures.  This
has led to a continuous release of both improvements in existing products and
the introduction of the Series 9600 Mobile Digital Imaging System in 1994 along
with the introduction in 1995 of the Uroview 2600, the Mini 6600 and the Compact
7600. In 1997 OEC introduced the 9600 Mobile Cardiac Cath Lab and the Mini 6600
Dual mode systems while in 1998 the Compact 7700 and the Series 7700 were
introduced.

   During 1998, 1997 and 1996, OEC's research and development expenses totaled
$13.0 million, $11.2 million and $8.9 million, respectively, representing 6.9%,
7.2% and 6.9% of net sales.

   Patents.  OEC's principle products are protected by patents, pending patents,
trade secrets, copyrights and similar rights which OEC believes adequately
protect its proprietary products.

                                       4
<PAGE>
 
   Employees.  On December 31, 1998, OEC had approximately 715 employees.  None
of OEC's employees are covered by collective bargaining agreements, and OEC
considers its employee relations to be satisfactory.

   Acquisitions.  During 1995, the Company purchased a 19.8% ownership position
in Barwig Medizinische Systeme GmbH (BMS), a German manufacturer of medical
equipment. On January 1, 1997, the Company purchased the remaining outstanding
shares of BMS, making it a wholly owned subsidiary of the Company and changing
the name to OEC Medizinische Systeme GmbH.  Costs associated with this
acquisition were not material.

   During 1998, the Company purchased a minority ownership position in Heartlab,
Inc., a Rhode Island based imaging software development company specializing in
cardiology.

   Risk Factors. The Company's business involves risks and uncertainties that
could cause actual results to differ materially from those projected. Such risks
and uncertainties include: product demand and market acceptance; the effect of
general economic conditions and foreign currency fluctuations; the impact of
competitive products and pricing; new product development and commercialization;
the effect of the continuing shift in growth from domestic to international
healthcare customers, the impact of managed care initiatives in the United
States and the ability to increase operating margins on higher sales.  Such
risks and uncertainties are fully discussed in the section labeled "Factors That
May Affect Future Results," appearing as pages 22 through 24 of Exhibit 13, the
Company's Annual Report to Stockholders.
 
Item 2.  Properties.

   OEC owns its corporate headquarters and manufacturing facility of 145,000
square feet in Salt Lake City, Utah, and leases another 80,000 square feet of
manufacturing in Warsaw, Indiana.  The lease expires on June 30, 2000.  The
Company has the right to renew this lease for another five years on similar
terms and conditions, if it so desires, and it also has the option to buy the
property.  The Company leases 30,000 square feet of manufacturing in
Wendelstein, Germany for the OEC GmbH operations. The lease expires in June
2000.  The Company also has the right to renew this lease on similar terms and
conditions at its discretion.

Item 3.  Legal Proceedings.
 
     A terminated distributor instituted litigation against the Company in 1986.
The trial court rendered an unfavorable decision in the amount of $3.1 million
in 1992. As a result of that decision, the Company established a reserve for the
judgment. The Company appealed the trial court decision on a number of grounds,
and in November 1993, the appellate court reversed the trial court and held for
the Company on the ground that the distributor had released his claims against
the Company in the settlement of other litigation and did not reach the other
issues raised on appeal. The distributor filed a petition in the Indiana Supreme
Court requesting that the court vacate the appellate court ruling and remand the
case to the appellate court for consideration of the other issues raised on
appeal. On December 31, 1996, the Indiana Supreme Court reversed the ruling of
the Indiana Circuit Court of Appeals and held that the trial court correctly
determined that the release executed by the distributor did not release the
Company. The case was remanded back to the appellate court for consideration of
the remaining issues raised on the appeal. On December 23, 1997 the appellate
court affirmed the trial court's judgement "in all matters except the
prejudgment interest which was reversed," and the Company appealed this
judgement to the Indiana Supreme Court. On October 30, 1998 the Indiana Supreme
Court denied the Company's petition to transfer.  The Company paid $4.9 million,
including interest, as final settlement of this matter.

   OEC is also a defendant in other ordinary commercial litigation.  In light of
available insurance and reserves, management believes that such litigation will
not have a material effect on OEC's business or financial condition.

Item 4.  Submission of Matters to a Vote of Security Holders.

   No matters were submitted to a vote of the Company's security holders during
the fourth quarter of fiscal year 1998.

                                       5
<PAGE>
 
                                    PART II
                                        
Item 5.  Market for Registrant's Common Equity and Related Stockholder Matters.

   The Company's common stock is presently traded on the New York Stock Exchange
under the trading symbol OXE.  Prices shown are the range of high and low
closing prices per share on the New York Stock Exchange -- Composite
Transactions, as reported by the Wall Street Journal.  On March 1, 1999, the
number of holders of record of common stock was 1,920.

              Prices
              ------
           Quarter Ended:         High       Low       Close
           -------------          ----       ---       -----
 
        March 31, 1997......    18 1/2      14 7/8    16 3/8
        June 30, 1997.......    17 15/16    13 3/8    17 13/16
        September 30, 1997..    19 3/8      15 3/8    18 7/8
        December 31, 1997...    20 13/16    16 11/16  19 15/16
 
        March 31, 1998......    24 7/16     19 3/16   23 5/8
        June 30, 1998.......    24 1/2      19 7/16   22 1/2
        September 30, 1998..    26 7/16     19 7/16   21 5/8
        December 31, 1998...    31 7/16     19 3/16   31 7/16
 

   The Company has not paid any dividends on its common stock.  The Company
presently intends to retain all earnings for use in the business and, therefore,
does not anticipate paying any cash dividends in the foreseeable future.


Item 6.  Selected Financial Data.

   The table labeled "Five Year Summary" appearing as page 18 of Exhibit 13, the
Company's Annual Report to Stockholders, is incorporated herein by reference.


Item 7.  Management's Discussion and Analysis of Financial Condition and Results
of Operations.

   The section labeled "Management's Discussion and Analysis of Financial
Condition and Results of Operations" appearing as pages 19 through 24 of Exhibit
13, the Company's Annual Report to Stockholders, is incorporated herein by
reference.


Item 7a. Quantitative and Qualitative Disclosures About Market Risk.

   The section labeled "Factors That May Affect Future Results" appearing as
pages 22 through 24 of Exhibit 13, the Company's Annual Report to Stockholders,
is incorporated herein by reference.


Item 8.  Financial Statements and Supplemental Data.

   The Consolidated Financial Statements and Notes thereto appearing at pages 25
through 35 of Exhibit 13, the Company's Annual Report to Stockholders, are
incorporated herein by reference.

 
Item 9.  Changes In and Disagreements with Accountants on Accounting and
Financial Disclosure.

   Not applicable.

                                       6
<PAGE>
 
                                   PART III
                                        
Item 10. Directors and Executive Officers of Registrant.

   Information concerning the directors of the Company is incorporated by
reference to the sections titled "Information with Respect to Nominees" in the
definitive Proxy Statement to be filed in connection with the Annual Meeting of
Stockholders (the "1999 Proxy Statement").   Information regarding executive
officers is set forth as follows:

Executive Officers of the Registrant
 
Name                         Age  Position
----                         ---  --------
 
Joseph W. Pepper              52  President and Chief Executive Officer
Randy W. Zundel               43  Chief Operating Officer, Chief         
                                  Financial Officer Executive Vice President
Barry K. Hanover              44  Chief Technical Officer & Executive Vice
                                  President, Engineering
Larry E. Harrawood            51  Executive Vice President, Clinical &
                                  Market Development
F. Daniel Edwards             43  Vice President, US Sales and Sales
                                  Support Marketing
Ted L. Parrot                 57  Vice President, Regulatory Affairs &
                                  Quality Assurance
Clarence R. Verhoef           43  Vice President,
                                  Finance, Treasurer & Secretary

   Joseph W. Pepper was named President and Chief Executive Officer, and
appointed to the Board of Directors of OEC Medical Systems, Inc., in May of
1997.  Prior to joining OEC, he was President of the Medical Devices Division of
Ohmeda, Inc., from 1995 to 1997.  From 1992 to 1995, he was President of
Ohmeda's Medical Systems Division, and, from 1988 to 1992, he was Vice President
in charge of the Monitoring Business Unit.  Prior to that time, Mr. Pepper held
engineering management positions at General Electric and at the Electric Power
Research Institute.  He is a director on the board of Heartlab, Inc.
 
   Randy W. Zundel is an Executive Vice President and the Chief Operating
Officer and the Chief Financial Officer of the Company.  He was appointed Chief
Operating Officer in September 1996. He has been the Chief Financial Officer of
the Company since October 1993. He was the Chief Operating Officer from February
1990 to September 1993.  Prior to that he was Vice President, Operations from
May 1987 to February 1990.  Mr. Zundel has held various other positions with OEC
since 1981.

   Barry K. Hanover is the Chief Technical Officer and Executive Vice President,
Engineering of the Company. He was appointed Chief Technical Officer in
September 1996. He has been the Vice President, Engineering since December 1992.
Previously, he was Director, Mechanical Engineering from October 1992 to
December 1992.  Prior to that, he was President of Hanover Engineering Services,
an engineering consulting firm, from June 1992 to October 1992, and Vice
President, Technical Development and member of the Board of Directors of Sarcos,
Inc., a biomedical technology company from 1988 through 1992.

   Larry E. Harrawood has been Executive Vice President, Clinical & Market
Development of the Company since July 1998, before which he was Vice President,
Marketing & Business Development since October 1986.  He was Vice President,
Sales and Marketing from July 1985 to October 1986, and General Manager of X-ray
operations from December 1972 to July 1985.

   F. Daniel Edwards was named Vice President, US Sales & Sales Support
Marketing in October 1998.  From January 1996 to October 1998, he held the
position of National Sales Manager of the Company.  Before that, he held various
sales and marketing positions at OEC since joining the Company in May 1988.  He
has over 20 years experience in the medical imaging industry, including sales,
marketing and technical service operations.

                                       7
<PAGE>
 
   Ted L. Parrot was named Vice President, Quality Systems and Regulatory
Affairs in 1994.  Prior to joining OEC, he held various positions at PPG
Biomedical Systems including Director of Marketing, Director of Engineering and
Director of Quality Assurance and Regulatory Affairs. He has 30 years experience
in the field of diagnostic imaging including 20 years with Philips Medical
Systems.

   Clarence R. Verhoef has been Vice President, Finance since September 1996 and
Treasurer since October 1993.  He was appointed Secretary in March 1998.  Mr.
Verhoef held the positions of Director of Finance from August 1993 to September
1996, Assistant Secretary from August 1993 to March 1998 and Controller from
October 1989 to August 1993.  He has held various other positions with OEC since
1977.

   Pursuant to Section 16(b) of the Securities Act of 1934, the Company's
directors, its executive (and certain other) officers, and any persons holding
more than 10 percent of the Company's stock are required to report their
ownership and any changes in beneficial ownership of the Company's stock to the
Securities and Exchange Commission and to the New York Stock Exchange.  Specific
due dates for these reports have been established and the Company is required to
report any failure to file by these dates.

Item 11. Executive Compensation.

   Information concerning management compensation is incorporated by reference
to the section titled "Cash Compensation of Executive Officers" in the 1999
Proxy Statement.

Item 12. Security Ownership of Certain Beneficial Owners and Management.

   Information concerning the stock ownership of each person known to the
Company to be a beneficial owner of five percent or more of the Company's Common
Stock and management is incorporated by reference to the sections titled
"Information with Respect to Nominees" and "Principal Stockholders" in the 1999
Proxy Statement.

Item 13. Certain Relationships and Related Transactions.

   Information concerning relationships and related transactions is incorporated
by reference to the section titled "Transactions with Management and Others" in
the 1999 Proxy Statement.


                                    PART IV
 
Item 14. Exhibits, Financial Statement Schedules and Reports on Form 8-K.

   (a)   1. Index to Financial Statements
 
   The following consolidated financial statements of the Company are included
in Exhibit 13 of this Form 10-K:


                                                                        Page in
                                                                      Exhibit 13
                                                                      ----------
Consolidated statements of operations for each of
 the three years in the period ended December 31, 1998..................... 25 
                                                                              
Consolidated balance sheets at December 31, 1998 and 1997.................. 26 
                                                                              
Consolidated statements of stockholders' equity for                           
 each of the three years in the period ended December 31, 1998............. 27 
                                                                              
Consolidated statements of cash flows for each of                             
 the three years in the period ended December 31, 1998..................... 28 
                                                                              
Notes to consolidated financial statements................................. 29 
                                                                              
Independent Auditors' Report............................................... 36 

                                       8
<PAGE>
 
       2. Index to Financial Statement Schedule

   All schedules have been omitted since the required information is not present
or is not present in amounts sufficient to require submission of the schedule,
or because the information required is included in the consolidated financial
statements, including the notes thereto.

       3. Index to Exhibits

   The following exhibits (numbered in accordance with Item 601 of SEC
Regulation S-K) are filed as part of this report or are incorporated by
reference as indicated below.

 Exhibit
 Number                      Description
 --------                    -----------


  3.1  Certificate of Incorporation, as amended. Incorporated by reference to
       the OEC Medical Systems, Inc. Form 10-K, filed March 30, 1994.

  3.2  By-Laws, as amended May 15, 1997. Incorporated by reference to the OEC
       Medical Systems, Inc. Form 10-Q, filed August 8, 1997.

 10.1  Diasonics, Inc. 1979 Stock Option Plan, amended and restated as of June
       1, 1982. Incorporated by reference to Exhibit 10.6 of the Diasonics, Inc.
       Registration Statement on Form S-8, filed May 2, 1983.

 10.4  Diasonics, Inc. 1990 Stock Option/Stock Purchase Plan. Incorporated by
       reference to Exhibit 10.79 of the Diasonics, Inc. Form S-8, filed on May
       1, 1991.

10.14  Form of Option Agreement used in connection with options having service-
       vesting provisions. Incorporated by reference to the OEC Medical Systems,
       Inc. Form S-8, filed June 12, 1998.

10.15  Form of Option Agreement used in connection with options having milestone
       provisions. Incorporated by reference to the OEC Medical Systems, Inc.
       Form S-8, filed June 12, 1998.

10.16  Form of Option Agreement used in connection with automatic option grant
       program for non-employee directors. Incorporated by reference to the OEC
       Medical Systems, Inc. Form S-8, filed June 12, 1998.

10.20  Form of Warrant Agreement used in connection with grant to independent
       contractors for the purchase of common shares. Incorporated by reference
       to the OEC Medical Systems, Inc. Form 10-K, filed March 27, 1997.

10.21  Agreement dated December 17, 1996, to acquire full ownership of Barwig
       Medizinische Systeme GmbH (BMS). Incorporated by reference to the OEC
       Medical Systems, Inc. Form 10-K, filed March 27, 1997.

10.24  OEC Medical Systems, Inc. 1993 Employee Incentive Stock Acquisition Plan,
       as amended and restated March 31, 1998. Incorporated by reference to the
       OEC Medical Systems, Inc. Form S-8 filed June 12, 1998.

10.25  OEC Medical Systems, Inc. 1998 Stock Option Plan. Incorporated by
       reference to the OEC Medical Systems, Inc. Form S-8, filed June 12, 1998.

10.26  Form of Option Agreement used in connection with the granting of
       incentive stock options. Incorporated by reference to the OEC Medical
       Systems, Inc. Form S-8, filed June 12, 1998.

11     Statement of Computation of Per Share Earnings.

                                       9
<PAGE>
 
13     Portions of the 1998 Annual Report to Shareholders, including Five Year
       Summary, Management's Discussion & Analysis of Financial Condition and
       Results of Operations, and Consolidated Financial Statements and Notes
       thereto.

21     List of Subsidiaries. Incorporated by reference to the OEC Medical
       Systems, Inc. Form 10-Q, filed May 13, 1997.

23     Independent Auditor's Consent.

27     Financial Data Schedule (FDS) for Edgar Filing.

       (b)  Reports on Form 8-K:
            Not applicable

                                       10
<PAGE>
 
                                  SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) 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.
 
                                 OEC MEDICAL SYSTEMS, INC.

                                 By:   /s/ Randy W. Zundel
                                    ----------------------------------
                                       Randy W. Zundel

                                 Executive Vice President & Chief Financial
                                        Officer


                               POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears
below constitutes and appoints Joseph W. Pepper and Clarence R. Verhoef and each
of them, as his true and lawful attorneys-in-fact and agents, with full power of
substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities, to sign any and all amendments (including post-effective
amendments) to this Report and form 10-K, and to file the same, with all
exhibits thereto, and other documents in connection therewith, with the
Securities and Exchange Commission, granting unto said attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite and necessary to be done in connection therewith,
as fully to all intents and purposes as he might or could do in person, hereby
ratifying and confirming all that said attorneys-in-fact and agents, or any of
them, or their or his substitute or substitutes, may lawfully do or cause to be
done by virtue hereof.

Date:  March 24, 1999

  Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed below by the following persons on behalf of the
registrant and in the capacities and on the date indicated.


  /s/ Ruediger Naumann-Etienne   Chairman of the Board         March 24, 1999
-------------------------------                                              
    Ruediger Naumann-Etienne                                                 
                                                                             
                                                                             
    /s/ Gregory K. Hinckley          Director                  March 24, 1999
-------------------------------                                              
      Gregory K. Hinckley                                                    
                                                                             
                                                                             
      /s/ Benno P. Lotz              Director                  March 24, 1999
-------------------------------                                              
       Benno P. Lotz                                                         
                                                                             
                                                                             
      /s/ Allan W. May               Director                  March 24, 1999
-------------------------------                                              
       Allan W.  May                                                         
                                                                             
                                                                             
     /s/ Chase N. Peterson           Director                  March 24, 1999
-------------------------------                                              
      Chase N. Peterson                                                      
                                                                             
                                                                             
     /s/ Joseph W. Pepper            Director                  March 24, 1999
-------------------------------                                              
      Joseph W. Pepper               President & CEO                         
                                                                             
                                                                             
     /s/ Randy W. Zundel             Principal Financial &     March 24, 1999 
-------------------------------                                              
      Randy W. Zundel                Accounting Officer   

                                       11