To analyze prescribing patterns of chronic psychiatric patients living in sheltered housing facilities, to identify the extent of polypharmacy and to estimate associated risks in this patient group. In a retrospective cross-sectional study the prescription data of 323 chronic psychiatric patients (average age 48.5 years) living in sheltered housing facilities in Rotterdam, The Netherlands, were analyzed. Prescription data were obtained from pharmacy-dispensing records. Patients received on average 4.6 drugs (95% CI, 4.3-4.9). The most frequently prescribed drugs were as expected antipsychotics, benzodiazepines and antimuscarinic drugs. Overall 25% (n=81) of patients received two or more antipsychotic drugs. A high proportion of patients (38%, n=124) received one benzodiazepine, and 15% (n=50) received two or more benzodiazepines. Patients in our study received a worryingly high number of drugs, and a quarter of the population was subject to antipsychotic polypharmacy. This increases the risk that drug-drug interactions, adverse drug reactions and noncompliance occur. Our study indicates potentially low quality of prescribing and shows the need for reviewing and special monitoring of pharmacotherapy in this patient group.