The “personal characteristics” and “extreme event” hypotheses have been proposed as alternative explanations for the development of posttraumatic stress disorder (PTSD) among combat veterans. The person-event interaction model attempts to integrate both perspectives by hypothesizing that premilitary individual vulnerability characteristics play a greater role in influencing risk of PTSD or PTSD symptom severity at lower than at higher levels of exposure to traumatic combat stressors. Focusing on a sample of 57 Vietnam veterans undergoing inpatient treatment for diagnosed PTSD, we assessed this model by examining interactions between negative parenting behaviors in childhood (e.g.-test), inconsistent love) and degree of combat exposure in predicting PTSD symptom severity. Hierarchical regression analyses supported the model, indicating that the father's negative parenting behaviors were more predictive of PTSD symptom severity at relatively lower levels of combat exposure. Implications of the findings for further research on multivariate, interactional models of PTSD etiology among Vietnam combat veterans are discussed.