This multisite study tested the ability of psychophysiological responding to predict posttraumatic stress disorder (PTSD) diagnosis (current, lifetime, or never) in a large sample of male Vietnam veterans. Predictor variables for a logistic regression equation were drawn from a challenge task involving scenes of combat. The equation was tested and cross-validated demonstrating correct classification of approximately 2/3 of the current and never PTSD participants. Results replicate the finding of heightened psychophysiological responding to trauma-related cues by individuals with current PTSD, as well as differences in a variety of other domains between groups with and without the disorder. Follow-up analyses indicate that veterans with current PTSD who do not react physiologically to the challenge task manifest less reexperiencing symptoms, depression, and guilt. Discussion addresses the value of psychophysiological measures for assessment of PTSD.