BACKGROUND Although the framework of the episode of care offers much promise in examining the process of primary health care, the development of episode-oriented, automated data sources has proceeded slowly. Experience with the International Classification of Primary Care (ICPC) in the European Community has confirmed its usefulness in creating and analyzing episodes of care, but it has seen little use in the United States. We describe the development of a Primary Care Information System (PCIS), which employs ICPC to create episodes of care from routinely collected clinical data. METHODS The PCIS is a partially computerized medical information system running on a standard Macintosh microcomputer. The PCIS integrates ICPC, ICD-9-CM, and CPT-4 coding structures to provide episode-oriented data for clinical, administrative, research, and reimbursement needs. The performance of the PCIS was assessed based on five major issues: clinician cooperation, data-entry accuracy, validity of episode data, cost, and perceived value to users. RESULTS The data collection and entry process required minimal additional effort from clinicians and data-entry personnel, and data-entry accuracy exceeded published estimates for other primary care data sources. Data management costs of about $1 per encounter compare favorably to published estimates for other office-based clinical information systems. The major problem seen during pilot testing was inaccurate tracking of episode boundaries through changes in providers and consequent changes in labels for problems and diagnoses. This problem has been addressed in development of the second-generation PCIS. CONCLUSIONS The combination of an episode-oriented framework such as ICPC and a flexible medical information system provides a promising platform for the study of the content and process of primary health care.