To improve detection and management of diabetes at a community mental health center, a cross-sectional study of the prevalence and management of type 2 diabetes mellitus was conducted among patients receiving maintenance antipsychotic medication (N=494). Diabetes was more than two-and-a-half times as prevalent among participants (17.4%) as in the general population. Fourteen percent of patients classified as diabetic had previously undiagnosed disease, compared with national sample rates of over 30%. Impaired fasting glucose was found for 26% of the sample. Glucose dysregulation was common. The known poor cardiovascular profile of persons with serious mental illness, reflected in the high rates of tobacco use and obesity in the sample, requires contextualizing efforts to screen and monitor for diabetes within overall efforts to monitor cardiovascular health.