We estimated the cost and cost-effectiveness of a clinical pharmacist intervention known to improve the appropriateness of drug prescribing. Elderly veteran outpatients prescribed at least five drugs were randomized to an intervention (105 patients) or control (103) group and followed for 1 year. The intervention pharmacist provided advice to patients and their physicians during all general medicine visits. Mean fixed and variable costs/intervention patient were $36 and $84, respectively. Health services use and costs were comparable between groups. Intervention costs ranged from $7.50-30/patient/unit change in drug appropriateness. The cost to improve the appropriateness of drug prescribing is thus relatively low.