Background: This article studied the factor structure of the Impact of Event Scale-Revised (IES-R) in two samples in Peru, i.e., a sample of survivors of a fire (N = 174) and a university student sample (N = 562). Methods: First, confirmatory factor analysis was used to compare nine different models of posttraumatic stress disorder symptoms as evaluated by the IES-R in both of the samples separately. The model with the best fit in both samples had four correlated factors, i.e., Intrusion, Avoidance, Hyperarousal and Sleep Disturbance. Second, the degree of factorial invariance of the IES-R was compared in both the samples using multiple group confirmatory factor analysis. Results and Conclusions: The results showed almost no differences between both samples. Finally, the results supported the internal consistency, as well as the concurrent and convergent validity of the IES-R in Peru. © 2009 Wiley-Liss, Inc.