This study sought to examine the impact of personality factors on symptom change following treatment for 141 Vietnam veterans with chronic combat-related posttraumatic stress disorder (PTSD) using the Minnesota Multiphasic Personality Inventory-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989). A series of partial correlation and linear multivariate regression analyses identified social alienation, associated with anger and substance use, as the most potent negative predictor of symptom change. Of the scales assessing personality disorder, Borderline Personality was identified as the strongest negative predictor of outcome. Regression analyses examining the most salient scales identified 5 items that contributed 14% of the variance in the prediction of change scores independently of the 21% accounted for by pretreatment PTSD severity.