The effects of a medication-monitoring service provided by a pharmacist in a congregate housing facility for geriatric patients were evaluated. A medication-monitoring service was provided by a clinical pharmacist to geriatric patients in two congregate housing facilities during an 18-month period. Patients were offered the service if they had histories of noncompliance and were referred for this reason to the study by physicians, staff, or family. The clinical pharmacist made weekly visits to each patient for assessment and provision of instructions and reinforcement regarding medication compliance. Medications were provided in special reminder packages prepared by a technician, and cost data for both materials and time were recorded. A total of 14 patients were referred to the study and received services for at least three months. Eight of these patients received services for one year. The costs of providing the service were $33/patient/month for personnel and $2/patient/month for materials. An 82-100% compliance rate was recorded; the mean compliance rate was 96%. Patients or their legal representatives paid the pharmacist directly for costs incurred. A medication-monitoring service is useful for geriatric patients whose primary limitation is inability to administer their own medications.