Background: a physician' s personal and professional characteristics constitute only one, and not necessarily the most important, determining factor of clinical performance. our study assessed how physician, organizational and systemic factors affect family physicians' performance. Method: our study examined 532 family practitioners who were randomly selected for peer assessment by the College of Physicians and surgeons of ontario. a series of multivariate regression analyses examined the impact of physician factors (e.g., demographics, certification) on performance scores in five clinical areas: acute care, chronic conditions, continuity of care and referrals, well care and records. a second series of regressions examined the simultaneous effects of physician, organizational (e.g., practice volume, hours worked, solo practice) and systemic factors (e.g., northern practice location, community size, physician-to-population ratio). Results: our study had three key findings: (a) physician factors significantly influence performance but do not appear to be nearly as important as previously thought; (b) organizational and systemic factors have significant effects on performance after the effects of physician factors are controlled; and (c) physician, organizational and systemic factors have varying effects across different dimensions of clinical performance. Conclusions: We discuss the implications of our results for performance improvement and physician governance insofar as both need to consider the broader environmental context of medical practice.