This is a study of physicians' stop-smoking advice to patients in a university-affiliated family medicine outpatient center. The study population consisted of 311 cigarette-smoking patients of 28 family-practice residents. Patients were monitored for three months to assess changes in their smoking habits and to measure the effects of advice from their physicians. Reports of advice were correlated with both patient and physician characteristics. Forty-one percent of the patients said they had been told by their physician to stop smoking during the three-month follow-up period. Heavy smokers (more than 26 cigarettes a day) (p = .02) and those being treated for tobacco-related conditions (p = .06) were most likely to report that their physician had advised them to quit smoking. Patients seen by a physician who was a cigarette smoker were less likely to report stop-smoking advice than patients seen by a nonsmoking physician (26 percent versus 44 percent, p = .02). Selectivity in the types of patients advised to quit smoking appears to reflect the physicians' personal judgments about the patients' likelihood of following their advice.