Efforts to improve the outcomes of patients with mental illness often have involved incorporating the skills of a variety of health care professionals into collaborative care models. For over 30 years, clinical pharmacists have contributed to these care models in capacities ranging from educator to consultant to provider. This systematic review evaluates the quantity and quality of medical literature examining the impact of pharmacists in mental health from 1972-2003. Although we identified approximately 35 publications describing the roles of clinical pharmacists in this regard, only 16 were of sufficient scientific rigor to permit evaluation and comparison. The 16 studies were divided equally between inpatient and outpatient settings and were conducted in a variety of health care organizations (e.g., Veterans Administration, health maintenance organizations, community mental health clinics, and nursing homes). Nine of the studies examined the role of pharmacists in providing treatment recommendations and patient education, five featured pharmacists as providers (with prescriptive authority), and the remaining two described the impact pharmacists have in delivering education to the psychiatric staff. Six of the 16 studies were prospective, but only three of these incorporated a randomization procedure for patients or facilities. Collectively, the results of the 16 studies were positive, demonstrating improvements in outcomes, prescribing practices, patient satisfaction, and resource use. Unfortunately, most of the investigations were small, and significant limitations in study design limited further comparison. Given the long history and anecdotal success of pharmacists in mental health care settings, additional multicenter cost-effectiveness trials are warranted to further support the role of the psychiatric pharmacist.