This chapter reviews the data available on the relationship of substance abuse and posttraumatic stress disorder (PTSD). Delimiting the review to those studies of Vietnam veterans, we found that levels of combat exposure seemed to be positively related to subsequent alcohol use, although not all studies confirmed this relationship. When studies of patients seeking treatment for PTSD were examined, we learned that 60-80% of these patients had concurrent diagnoses of substance abuse, alcohol abuse, or dependence. Methodological limitations of all the studies are discussed and conclusions regarding the status of the PTSD-substance abuse relationship are drawn cautiously. Alternative suggestions for treatment are presented and discussed.