The study determined the separate and joint effects of 1) physician specialty, 2) type of medical school attended, 3) time in practice, 4) type of ambulatory care setting, and 5) type of hospital on the quality of physician performance in patient care. The sample consisted of 454 physicians in 18 specialty categories. Multiple Classification Analysis was used to determine the effects of these predictors on the quality of physician performance. The study found that the organization of hospital care had a large independent effect, but that the other four predictors had relatively small effects on the quality of physician performance. The findings imply that the organization of the setting in which care is provided has more influence than the education and training that physicians had attained. All five predictors together explained 20 per cent of the variance. Methodological suggestions were made to improve the explanatory power of the variables, and various pragmatic for medical care administrators were presented.