A study was conducted to further investigate whether the Keane Posttraumatic Stress Disorder (PTSD) Scale of the Minnesota Multiphasic Personality Inventory (MMPI) can be employed as a separate instrument administered outside the context of the full MMPI. A group of Vietnam combat veterans with diagnosed PTSD and two comparison groups of veterans without PTSD (Vietnam combat and era veterans) were diagnosed by clinical interviews. Over 84% of the 64 veterans in the study were accurately classified by the Keane PTSD Scale into their original diagnostic groups. Excellent test sensitivity was demonstrated, with 90% of combat veterans with PTSD being properly classified by the Keane PTSD Scale when the recommended cutoff score of 30 was utilized. The clinical and research implications are discussed.