Lack of information on medication is one of the main reasons why some 30-50% of patients fail to take their medicines as prescribed. To assess patient knowledge about prescribed drugs, outpatients from an internal medicine clinic in a teaching hospital were interviewed after medical consultation. Patients were asked to identify the name, indication, dosage, administration schedule, duration of treatment, side effects, and precautions. Patients' answers were compared to medical prescription or patients' medical records. Two hundred and sixty-four patients were interviewed, of whom 34% displayed satisfactory knowledge. In 31% of cases the drug name stated was incorrect, while in 19% the reported indication differed from that on the medical records. Dosage and administration schedules stated by patients disagreed with physician's instructions in 19% and 31% of cases, respectively. The results suggest that the majority of outpatients have sufficient knowledge for the safe use of prescribed drugs, under an ideal outpatient setting.