This study examined the effects of Vietnam war-zone duty and combat-related posttraumatic stress disorder (PTSD) on severity of drug- and alcohol-abuse disorders among veterans seeking treatment for substance dependence. Combat-exposed Vietnam-theater veterans (N = 108) were compared with Vietnam-era veterans without war-zone duty (N = 151) on psychometric measures of drug and alcohol abuse. There were no differences between theater and era veterans on these measures. However, Vietnam-theater veterans with PTSD experienced more severe drug- and alcohol-abuse problems than did theater veterans without PTSD and were at greater risk for having both forms of substance abuse. Further analyses showed that PTSD was significantly related to some dimensions of drug- and alcohol-abuse problems but not to other dimensions. These findings indicate that PTSD, rather than combat stress per se, is linked to severity of substance abuse. Finally, reexperiencing and avoidance/numbing components of PTSD were more strongly associated with drug abuse than alcohol abuse, but physiological arousal symptoms of PTSD were more highly correlated with alcohol abuse.