This study's purpose was to evaluate the prevalence and correlates of posttraumatic stress disorder (PTSD) in persons with severe mental illness. Standardized assessments of interpersonal trauma and PTSD were conducted in 782 patients with severe mental illness receiving services in one of five inpatient and outpatient treatment settings. Analyses examined the prevalence of PTSD and the demographic, clinical, and health correlates of PTSD diagnosis. The overall rate of current PTSD in the sample was 34.8 percent. For demographic characteristics, the prevalence of PTSD was higher in patients who were younger, white, homeless, and unemployed. For clinical and health variables, PTSD was more common in patients with major mood disorders (compared to schizophrenia or schizoaffective disorders), alcohol use disorder, more recent psychiatric hospitalizations, more health problems, more visits to doctors for health problems, and more nonpsychiatric hospitalizations over the past year. The results support prior research documenting the high rates of PTSD in patients with severe mental illness and suggest that PTSD may contribute to substance abuse, psychiatric and medical comorbidity, and psychiatric and health service utilization.