This study investigated the psychometric properties of the Impact of Event Scale -- Revised (IES-R) in two samples of male Vietnam veterans: a treatment-seeking sample with a confirmed posttraumatic stress disorder (PTSD) diagnosis (N = 120) and a community sample with varying levels of traumatic stress symptomatolgy (N = 154). The scale showed high internal consistency (alpha = 0.96). Confirmatory factor analysis did not provide support for a three-factor solution corresponding to the three subscales of intrusion, avoidance, and hyperarousal. Exploratory factor analysis suggested that either a single, or a two-factor solution (intrusion/hyperarousal and avoidance), provide the best account of date. However, correlations among the subscales were higher in the community sample than in the treatment sample, suggesting that the IES-R may be sensitive to a more general construct of traumatic stress in those with lower symptom levels. The correlation between the IES-R and the PTSD Checklist was high (0.84) and a cutoff of 1.5 (equivalent to a total score of 33) was found to provide the best diagnostic accuracy.