This paper focuses upon problematic patterns of thought and behavior among Vietnam combat veterans identified with Post-traumatic Stress Disorder which are associated with difficulties in emotional, interpersonal, and vocational functioning. The following patterns have been identified: intolerance of mistakes, denial of personal difficulties, anger as a problem-solving strategy, hypervigilance, and absolutistic thinking. The realistic and adaptive origins of these patterns in the combat enviroment are identified, and their maladaptiveness outside the combat enviroment is described. Consideration is also given to why such patterns persist years after the last combat experience. Finally, the implications for psychotherapy of the verteran with PTSD are discussed.