The authors describe the changes in DSM-III criteria for posttraumatic stress disorder (PTSD) that have been included in DSM-III-R. DSM-III-R includes specification of generic characteristics of traumatic stressors, clearer organization of symptoms around three dimensions of stress response (reexperiencing, avoidance and numbing, and physiological arousal), inclusion of symptoms specific to children, and specification of onset and duration of the disorder. The importance of these changes in the evolution of the diagnosis of PTSD is discussed.