OBJECTIVES: To determine how often primary care physicians discuss medication costs with their senior patients and what cost-reducing strategies they employ. DESIGN: Cross-sectional, random-sample mail questionnaire. SETTING: State of California. PARTICIPANTS: Six hundred seventy-eight of 1,098 (62%) internal medicine and family practice physicians selected from the American Medical Association Masterfile. MEASUREMENTS: Main outcomes included frequency of cost discussions with senior patients in the previous 30 days and choice of cost-reducing strategy when a senior expresses financial difficulty with medication costs. RESULTS: Forty-three percent of physicians reported discussing medication cost with at least half of their senior patients in the previous 30 days. Patients initiated most of these discussions. Forty percent reported that, at least one time in the previous 30 days, they had not discussed cost but wished they had. The most common reason given was "I ran out of time" (36%). Physicians with high perceived knowledge of medication costs were more likely to discuss cost (odds ratio (OR)=3.49, 95% confidence interval (CI)=1.66-7.3) versus low perceived knowledge, but this trend was not seen in physicians who scored high on actual knowledge of medication costs (OR=0.78, 95% CI=0.43-1.43) versus low actual knowledge. The most common cost-reducing strategies were generic substitution (33%) and offering samples (25%). CONCLUSION: The frequency of medication cost discussions between physicians and senior patients is low, and when it occurs, is often initiated by patients. Physicians' perception of their knowledge of medication costs may be an important factor in initiating cost discussions.