Posttraumatic stress disorder (PTSD) is a prevalent disorder that adversely affects 2-5% of the general population. Little is known about PTSD in the primary care setting. The purpose of the present study was to evaluate the utility of a screening instrument for PTSD (the PCL-C) in primary care and to examine comorbidity, disability, and patterns of healthcare utilization among persons with PTSD in this setting. Adult, English-speaking patients attending for routine medical care (N=368) participated in a two-stage screening consisting of the administration of a self-report measure for posttraumatic stress disorder (the PCL-C) followed by a structured diagnostic interview. Current (1-month) prevalence of PTSD was determined, as were current comorbid disorders. Brief functional impairment and disability indices were administered, and healthcare utilization in the prior 6 months was ascertained. 11.8% (standard error 1.7%) of primary care attendees met diagnostic criteria for either full or partial PTSD. Comorbidity with major depression (61% of cases of PTSD) and generalized anxiety disorder (39%) was common, but less so with social phobia (17%) and panic disorder (6%). Substance use disorder comorbidity (22%) was also fairly common. Patients with PTSD reported significantly more functional impairment than patients without mental disorders. Patients with PTSD also made greater use of healthcare resources than not mentally ill patients. PTSD frequently is encountered in primary care, and is associated with considerable functional impairment and healthcare utilization. Comorbidity with other mood and anxiety disorders is extensive. It remains to be seen if greater awareness and more aggressive treatment of PTSD in primary care will lead to improved functioning and reduced (or more appropriate) healthcare utilization. These are topics for further study.