OBJECTIVE: The purpose of the study was to evaluate the prevalence of posttraumatic stress disorder (PTSD) among substance users in the general population. METHOD: The St. Louis Epidemiologic Catchment Area study, a survey of psychiatric illness in the general population, collected data on PTSD and substance use with the Diagnostic Interview Schedule. Among the 2,663 respondents, 430 reported a traumatic event that could qualify for PTSD; however, the rate of PTSD was low, 1.35% overall. To evaluate the relationship between PTSD and substance use, respondents were hierarchically classified into one of four substance use categories ranging from polydrug use to alcohol use only. Substance users from each category as well as substance users in general were compared with persons who did not meet the substance use threshold (comparison subjects). RESULTS: Findings indicate that cocaine/opiate users are over three times as likely as comparison subjects to report a traumatic event, report more symptoms and events, and are more likely to meet diagnostic criteria for PTSD. Physical attack, but not combat- related events, was the most prevalent event reported among cocaine/opiate users. Onset of substance use preceded onset of posttraumatic symptoms, suggesting that substance use predisposes the individual to exposure to traumatic events. When other variables-- including antisocial behavior--were controlled, female gender and use of cocaine/opiates predicted PTSD. CONCLUSIONS: These analyses of the co-occurrence of substance abuse and PTSD warrant further study and suggest that PTSD is much more common among substance abusers than was previously known.Abstract Teaser