Controversy exists regarding the rate and risk factors for posttraumatic stress disorder (PTSD) following traumatic brain injury (TBI). The authors determined the rate and phenomenology of PTSD symptoms in the 6 months after TBI by conducting a prospective cohort study of 124 subjects who completed the PTSD Checklist-Civilian Version. The cumulative incidence of meeting PTSD symptom criteria at 6 months was 11% and full criteria 5.6%. Prevalence peaked at 1 month (10%). Eighty-six percent had another psychiatric disorder and 29% a history of PTSD. Symptoms were associated with not completing high school, assault, recalling being terrified or helpless, and positive toxicology. PTSD after TBI is rare and the relation to risk factors and comorbidities must be examined.