Objectives : The three symptom clusters of posttraumatic stress disorder (PTSD) are reexperience, avoidance, and hyperarousal. Alcohol use disorders frequently co-occur with PTSD, and possible functional correlations are suspected. Scholarly evaluation of the differences between the symptoms of PTSD and those of alcohol problems may be useful in understanding the pathophysiology of the comorbidity. Methods : We recruited Vietnam veterans with PTSD (n=97) and without PTSD (n=132). The alcohol use disorder identification test (AUDIT), and clinician-administered PTSD scale (CAPS) were administered to participants. The PTSD group was divided into two categories: those with PTSD only (n=57) and those with concurrent alcohol-related problems (n=40). Results : The PTSD group showed higher AUDIT scores compared to the control group. In the PTSD group, participants with alcohol problems had a severer symptoms of recurrent dream and sleep disturbance symptoms compared to the PTSD only group. No significant differences were found in the three major symptom clusters of PTSD. Conclusion : These findings support the proposed existence of a functional correlation between PTSD and alcohol use disorder. Clinicians should carefully evaluate and treat comorbid alcohol use disorder in patients with PTSD.