Medication errors (MEs) in psychiatry have not been extensively studied. No long-term prospective efforts to demonstrate error reduction in psychiatric care using multidisciplinary interventions have been published in the literature. This article discusses the implementation of the Patient Safety Net (PSN) (an error reporting system) and of the Provider Order Entry (POE) program (a prescribing system). We educated and trained staff in their use, conducted concurrent chart reviews to estimate true error reduction, and provided continuous feedback as errors occurred. The intervention described here resulted in a reduction in MEs in association with performance improvement efforts that were conducted over 5 years and involved 65,466 patient days, and 617,524 billed doses, which is the largest study of an intervention to reduce psychiatric medication errors reported to date.