At age 36, Vietnam veterans in the high school class of 1963 reported significantly more problems related to nightmares, loss of control over behavior, emotional numbing, withdrawal from the external environment, hyperalertness, anxiety, and depression than did their classmates matched with them on 51 high school characteristics. These problems correspond closely to the disorder labeled post-traumatic stress disorder (PTSD) by the American Psychiatric Association. PTSD was associated with other family, mental health, and social interaction problems. Some environmental variables--e.g., the presence of a spouse or being a churchgoer--were associated with reduced levels of PTSD or with reductions in the degree of association between combat and PTSD. The direction of cause and effect in these associations cannot be ascertained from our data, but it seems plausible to postulate that support factors can and do help some Vietnam veterans with PTSD.