Findings from the Congressionally mandated National Vietnam Veterans Readjustment Study indicate that nearly one-half million Vietnam veterans-15.2% of the men and 8.5% of the women who served in Vietnam-suffer from post-traumatic stress disorder (PTSD) fifteen or more years after their military service. Current PTSD prevalence rates for Vietnam veterans are significantly and substantially higher than the rates for their comparable Vietnam generation peers, which range from 0.3% to 2.5%. Additionally, the current prevalence rate among male Vietnam veterans was found to differ significantly among race/ethnicity subgroups: 27.9% among Hispanic men, 20.6% among black men, 13.7% among white/other men. Multivariate analyses indicated that although background factors are significantly related to the current prevalence of PTSD, the current prevalence is much higher among Vietnam veterans than among era veteran and civilian counterpart comparison groups even after background differences are taken into account. These analyses also demonstrated the important role of exposure to combat and other types of war zone stress in the current prevalence of the disorder. © 1992 Plenum Publishing Corporation.