We surveyed physicians of different specialties in a large metropolitan area to determine how their characteristics affected their performance and beliefs about breast cancer screening. Of 664 general internists, obstetrician-gynecologists, and cardiologists surveyed, we received 298 responses (45%). We found significant differences in reported performance of breast cancer screening and physicians' beliefs about mammography screening among practicing obstetrician-gynecologists, internists, and cardiopulmonary specialists. Cardiopulmonary specialists performed the fewest breast examinations and screening mammograms and were most likely to believe annual mammography screening unnecessary even for women in their 50s. We observed no difference between physicians graduating before 1960 and those graduating afterward and no differences according to physician sex. We found similar screening practices and beliefs in the three types of practice settings examined: community-based, private practices, a large health maintenance organization (HMO), and academic medical centers. Obstetrician-gynecologists and internists differed only in the frequency with which they performed breast examinations. Physicians graduating before 1960 in these two groups reported somewhat poorer performance and knowledge of breast cancer screening than those graduating more recently. A majority of all respondents disagreed with American Cancer Society guidelines for mammography screening. Physicians of all specialties reported performing far more breast examinations than screening mammograms on women of all ages, even for those 50-59 years of age. We conclude that all physicians need to improve their screening rates. However, intervention programs should first target those physicians with the greatest deficiencies in breast cancer screening performance and knowledge; these include medical specialists and older physicians in primary care specialties.