Hispanic veterans are said to exhibit higher risk of developing posttraumatic stress disorder (PTSD) than veterans of other racial/ethnic backgrounds. This prediction is based largely on findings from the National Vietnam Veterans Readjustment Study (NVVRS; R. A. Kulka et al., 1990a, 1990b). This article first summarizes the findings of the NVVRS with regard to race/ethnicity and PTSD, and then it makes a careful assessment of both the external and the internal validity of these findings. Conceptual issues are addressed and, where possible, further analyses of the NVVRS data set are conducted to identify factors that account for ethnic differences in rates of the disorder. Possible mediators of the effects of Hispanic ethnicity on vulnerability to PTSD are identified, including psychosocial factors (racial/ethnic discrimination and alienation) and sociocultural influences (stoicism and normalization of stress, alexithymia, and fatalism). Areas in which future research is needed are indicated.