The purpose of this study was to examine differences in work patterns and practice characteristics of male and female physicians using data from the American Medical Association's Twelfth Periodic Survey of Physicians conducted in 1978. Following are some of the major findings: Male physicians were more likely than female physicians to work either in the traditional solo, fee-for-service practice or in a group-practice setting. Female physicians were more likely to be found in some other setting such as a clinic, student health center, local government agency, or corporation and were more frequently reimbursed on a salary basis. Male physicians worked more hours per week (50.9 versus 43.7) and more weeks per year (47.1 versus 45.9) and were reimbursed at a higher annual level ($62,700 versus $43,700) than their female counterparts. Even if women worked the same number of hours per week and weeks per year as men, the mean income from medical practice for females would be 83% of the mean income for males. The differential, however, diminished over the five-year period between 1972 and 1977.