This research examines the DSM-IIIR criteria for posttraumatic stress disorder (PTSD). The study questions whether the psychiatric sequelae resulting from exposure to extraordinary traumatic events (stressor criterion A) do in fact differ from the sequelae resulting from exposure to more common yet stressful life experiences. The study also examines whether PTSD sequelae (criteria B-D) accurately describe the responses of victims even of extreme events fitting the DSM-III-R definition of stressor. The study included data from both St Louis victims exposed to floods and/or unsafe dioxin levels, and Puerto Rico victims of mudslides/flooding. Results showed that some of the common stressful events related more closely to PTSD symptoms than did the extraordinary events. Further, disaster exposure most strongly related to symptoms of reexperiencing (criterion B); symptoms relating to avoidance (criterion C) were particularly unreported. Results are discussed in terms of their implications for revision both of the PTSD criteria for DSM-IV, and of instruments designed to assess PTSD symptomatology.