Patients' preferences for physicians of a particular sex tend to skew sex distributions of clinical populations in training and practice settings. A study was developed to explore these preferences and potential reasons for them. Of 185 adult patients surveyed at four family practice residency clinics, 45% expressed a preference for sex of physician; 43% of women and 12% of men preferred a female physician, while 31% of men and 9% of women preferred a male physician. Patients who stated no overall preference often expressed one in specific clinical situations, eg, anal or genital examinations. Patients who preferred female physicians reported humane behaviors as more characteristic of female physicians, and those who preferred male physicians reported humane behaviors as more characteristic of men; patients who had no overall sex preference did not sex stereotype physicians on these behaviors (F = 59.34, P less than .01). Patients who preferred male physicians reported technical competence behaviors as more characteristic of male physicians; others did not sex stereotype physicians on these behaviors (F = 15.4, P less than .01). Patients rated humaneness and comprehensiveness as being of high priority, but no relationship was found between priorities for aspects of care and preferences for sex of physician. Areas for future investigation include assessing preferences in other populations and exploring sex differences in physician behavior during office encounters and correlating these differences with patient satisfaction.