This study employed data from two Congressionally mandated efforts (the American Indian Vietnam Veterans Project and the National Vietnam Veterans Readjustment Study) to examine differential prevalence of posttraumatic stress disorder (PTSD) among 5 ethnically defined samples of male Vietnam theater veterans. Lay interviews assessed individual experiences before, during, and after the war from 1,798 male Vietnam theater veterans. Clinical reinterviews using the SCID were conducted with subsamples (N = 487). The prevalence of both 1-month and lifetime PTSD was higher for the 2 American Indian samples than for Whites. Once logistic regressions controlled for differential exposure to war-zone stress, ethnicity was no longer a significant predictor of PTSD.