Table Of Contents

As filed with the Securities and Exchange Commission on April 24, 2003

Registration No. 333-            

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

IMPAC MEDICAL SYSTEMS, INC.

(Exact Name of Registrant as Specified in Its Charter)

100 West Evelyn Avenue, Mountain View, California 94041

(650) 623-8800

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Joseph K. Jachinowski

President and Chief Executive Officer

IMPAC Medical Systems, Inc.

100 West Evelyn Avenue

Mountain View, California 94041

(650) 623-8800

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Approximate date of commencement of proposed sale to the public:

As soon as practicable after this Registration Statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act, check the following box.  ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨                      

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨                      

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨                      

If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box.  ¨

CALCULATION OF REGISTRATION FEE

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until this Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

Table Of Contents

SUBJECT TO COMPLETION, DATED APRIL 24, 2003

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission  is effective. This prospectus is not an offer to sell these securities, and it is not soliciting an offer to buy these securities in any state or jurisdiction where the offer or sale is not permitted.

2,158,500 Shares

Common Stock

IMPAC Medical Systems, Inc. is selling 200,000 shares of common stock and the selling stockholders identified in this prospectus are selling an additional 1,958,500 shares. We will not receive any of the proceeds from the sale of the shares by the selling stockholders. The selling stockholders have granted the underwriters a 30-day option to purchase up to an additional 323,775 shares from them to cover over-allotments, if any.

Our common stock is traded on the Nasdaq National Market under the symbol “IMPC.” The last reported sale price on April 24, 2003 was $19.00 per share.

INVESTING IN OUR COMMON STOCK INVOLVES RISKS. SEE “RISK FACTORS” BEGINNING ON PAGE 7.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

Thomas Weisel Partners LLC

U.S. Bancorp Piper Jaffray

William Blair & Company

The date of this prospectus is                 , 2003

Table Of Contents

Table Of Contents

TABLE OF CONTENTS

You should rely only on the information contained or incorporated by reference in this prospectus. We have not authorized anyone to provide you with information different from that contained in this prospectus. We are offering to sell shares of common stock and seeking offers to buy shares of common stock only in jurisdictions where offers and sales are permitted. The information contained in this prospectus is accurate only as of the date of this prospectus, regardless of the time of delivery of this prospectus or of any sale of the common stock.

In this prospectus, “Company,” “we,” “us” and “our” refer to IMPAC Medical Systems, Inc. and its subsidiaries. Unless otherwise indicated, all information in this prospectus assumes no exercise of the underwriters’ over-allotment option.

Table Of Contents

PROSPECTUS SUMMARY

You should read the following summary together with the more detailed information concerning our company, the common stock being sold in this offering and our financial statements appearing in this prospectus. This prospectus contains forward-looking statements that involve risks and uncertainties. Because this is only a summary, you should read the rest of this prospectus before you invest in our common stock. Read this entire prospectus carefully, especially the risks described under “Risk Factors.”

IMPAC Medical Systems

We provide information technology systems for cancer care. Our systems provide electronic medical record, imaging, decision support, scheduling and billing applications in an integrated platform to manage the information-related complexities of cancer care, from detection and diagnosis through treatment and follow-up. Cancer centers require specialized information technology to administer complex treatments, to integrate advanced medical devices, to provide data aggregation and to meet reporting requirements. In addition to satisfying these needs, our systems improve the delivery of cancer care by enhancing patient safety, enabling advanced therapies, streamlining process management and facilitating communications.

We market and sell our systems to university teaching hospitals, community and government hospitals, freestanding cancer centers and private practices. Our information technology, or IT, solutions include point of care systems and cancer registry systems. In North America, we have sold and installed over 900 of our point of care systems and over 400 of our cancer registry systems in over 1,100 customer facilities. Based on our internal competitive analysis of the oncology IT market, we believe we have completed significantly more installations than our closest competitors. Our customers include 29 of the top 50 U.S. cancer hospitals, as ranked by U.S. News & World Report in July 2002. Outside of North America, our point of care systems are installed in approximately 400 facilities located in over 50 countries. Our modular design provides cancer centers the flexibility to fulfill their initial IT needs and easily expand their systems over time. We install our systems in facilities that range from small departments with less than five users to national delivery networks with hundreds of users.

Our business has grown steadily since our inception in 1990. Our net sales increased from $16.3 million for our fiscal year ended September 30, 1998 to $45.7 million for our fiscal year ended September 30, 2002, a compound annual growth rate of 29.3%. Our net sales increased from $20.4 million in the six months ended March 31, 2002 to $27.5 million in the six months ended March 31, 2003.

Industry Overview

Cancer is the second leading cause of death in the United States after heart disease. There are approximately 7,400 facilities in the United States that provide cancer treatment services. We believe there are also more than 4,000 accessible cancer treatment facilities outside the United States. These facilities provide surgery, chemotherapy and/or radiation therapy. Vendors in this market include companies whose primary business is oncology IT solutions, vendors who offer capital equipment with oncology IT solutions and healthcare IT providers that offer general solutions to all healthcare segments.

The treatment of cancer requires the precise coordination of many different healthcare practitioners who employ complex treatment methodologies, some of which can be extremely harmful or even fatal to the patient if administered improperly. These treatments are often administered in multiple settings

1

Table Of Contents

and over an extended period of time. Additionally, these processes have intensive information management and billing requirements.

Many healthcare IT systems provide basic administrative and clinical functions, but do not satisfy the specialized requirements of cancer care.

Our Solution

Our IT solution provides the following benefits:

Our Strategy

The key elements of our strategy are:

2

Table Of Contents

Corporate Information

We were incorporated in California as IMPAC Medical Systems, Inc. in January 1990, and we reincorporated as a Delaware corporation in November 2002. Our principal executive offices are located at 100 West Evelyn Avenue, Mountain View, California 94041, and our telephone number is (650) 623-8800. Our corporate website is www.impac.com. Information contained on our website does not constitute part of this prospectus.

IMPAC Medical Systems, Inc., IMPAC, the IMPAC logo and our product names are trademarks of IMPAC. All other brand names or trademarks appearing in this prospectus are the property of their respective holders.

3

Table Of Contents

THE OFFERING

Unless otherwise noted, the information in this prospectus, including the information above:

4

Table Of Contents

SUMMARY CONSOLIDATED FINANCIAL INFORMATION

(in thousands, except per share data)

The table below sets forth summary consolidated financial information for the periods indicated. This data has been derived from our audited consolidated financial statements for the years ended September 30, 2000, 2001 and 2002 and from our unaudited consolidated financial statements for the six months ended March 31, 2002 and 2003 and as of March 31, 2003 included elsewhere in this prospectus. The statements of operations data for the years ended September 30, 1998 and 1999 were derived from our audited consolidated financial statements that do not appear in this prospectus. It is important that you read this information together with the section entitled “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated financial statements and the notes to them included elsewhere in this prospectus.