DSM-III defined PTSD as a syndrome that follows exposure to a special class of stressors, that is, events that are outside the range of usual human experience. The definition of the PTSD stressor in DSM-III is ambiguous: It is unclear if it depends on a quantitative or qualitative difference. Furthermore, although a body of literature had described psychologic reactions to war and civilian catastrophes, there was at the time little empirical support for a strong and unique association between the PTSD symptom cluster and a special class of stressors. The revised definition of PTSD in DSM-III-R has not clarified the PTSD stressor criterion. However, changes were made in the criterial symptoms. Symptoms of avoidance were moved from the “Miscellaneous” to the “Numbing” category. The change was not based on empirical evidence; it was based instead on an untested psychologic paradigm about traumatic neurosis. Suggestions are made for future research to test the assumptions embedded in the PTSD definition.