Persons with serious mental illness have increased rates of chronic medical conditions, have limited access to primary care, and incur significant health care expenditures. Few studies have explored providing medical care for these patients in the ambulatory mental health setting. This study describes a real-world population of mental health patients receiving primary care services in a community mental health clinic to better understand how limited primary care resources are being utilized. Chart review was performed on patients receiving colocated primary care (colocation group, N = 143) and randomly chosen patients receiving mental health care only (mental-health group, N = 156) from January 2006 through June 2011. Demographic and mental and physical health variables were assessed. Compared to the mental-health group, the colocation patients had more psychiatric hospitalizations (mean = 1.07 vs 0.23, P < .01), were more likely to be homeless (P < .01), and were more likely to require intensive case management (P < .01). Interestingly, the colocation group was not more medically ill than the mental-health group on key metabolic measures, including mean body mass index (colocation = 27.8 vs mental-health = 28.7, P = .392), low-density liprotein (colocation = 110.0 vs mental-health = 104.4, P = .480), and glucose (colocation = 94.1 vs mental-health = 109.2, P = .059). The most common medical disorders in the colocation group were related to metabolic syndrome. Colocated primary care services were allocated on the basis of severity of psychiatric impairment rather than severity of medical illness. This program serves as a model for other systems to employ for integrated primary and behavioral health services for patients with serious mental illness.