OBJECTIVE: Studies indicate that chronic combat-related posttraumatic stress disorder (PTSD) is frequently associated with other psychiatric disorders. Questions regarding the nature and interrelationships of these conditions require clarification. The purpose of this study was to address primary and secondary illness relationships by focusing on the specific phenomenology and course of illness onset of PTSD comorbidity. METHOD: In order to minimize confounding factors, only outpatients without recent substance use disorders were included. Sixty subjects who had been exposed to severe combat stress including veterans of Vietnam and veterans of World War II or Korea, 15 of whom were former prisoners of war, received structured assessments over serial evaluations. RESULTS: PTSD was the most prevalent lifetime disorder followed by major depression, panic disorder, generalized anxiety disorder, and phobic disorder or symptoms. Endogenous-appearing features overlapping other clinical populations were common; however, some specific symptom patterns also were suggestive of traumatic influence. Unlike generalized anxiety disorder and past substance use, the mean onset of phobias, major depression, and panic disorder, respectively, occurred later than PTSD. CONCLUSIONS: These observations suggest that persistent conditions related to PTSD progress toward symptoms that are increasingly autonomous in their pattern of occurrence.Abstract Teaser