OBJECTIVE: In a group of crime victims, the authors investigated overlap between acute stress disorder and posttraumatic stress disorder (PTSD) diagnoses and their relative ability to predict PTSD at 6 months. METHOD: A mixed-sex group of 157 victims of violent assault were interviewed within 1 month of the crime. At the 6-month follow-up, 87.9% were reinterviewed by telephone. RESULTS: At baseline the rate of acute stress disorder was 19.1%, the rate of PTSD was 21.0%, and the percentage agreement between them was 95.5%. The two diagnoses were equally effective predictors of PTSD 6 months later. CONCLUSIONS: The high level of overlap between acute stress disorder and PTSD calls into question whether, as presently formulated, they represent distinct diagnoses.