Background: The aim of this study was to investigate predictors of persistent symptoms of posttraumatic stress disorder (PTSD) and to examine the construct validity of PTSD in a national sample of 270 World War II and Korean Conflict prisoners of war (POWs). Method: POWs were interviewed at two points in time (1965 and 1990). Predictors included PTSD symptomatology measured in 1965 by items from the Cornell Medical Index (CMI), severity of captivity trauma, resilience factors, and post-trauma social support. The criterion, symptomatology in the early 1990s, was evaluated with the PTSD module of the Structured Clinical Interview for DSM (SCID). Results: The CMI provided only partial coverage of PTSD criteria and appeared to provide only a general index of distress. Clustering of SCID items in two-dimensional space via multidimensional scaling analysis offers some construct validation for the DSM's differentiation of PTSD symptoms into criterion groups, although there was not a perfect match. Trauma severity is best related to PTSD symptomatology experienced in 1990, mitigated in part by greater education level and age at the time of trauma exposure. Surprisingly, 1965 distress added only a modest amount to the prediction of current distress, while post-trauma social support added none. Conclusions: These findings support previous work showing the severe psychological sequelae of POW status 40-50 years after captivity, and indicate that trauma severity during captivity is the best predictor of current PTSD symptomatology. Results also add to our understanding of the conceptual differentiation of PTSD symptoms into separate and distinct symptom clusters.