• The new diagnostic nomenclature of the American Psychiatric Association (DSM-III) provides well-described categories of stress response syndromes that were not included in the previous nosology. The signs and symptoms of these syndromes used in the descriptive statements have been understood largely in terms of field studies of nonpatient populations and clinical descriptive and impressionistic studies of patient populations. We report quantitative data from the study of a population with post-traumatic stress disorder. The results confirm clinical impressions of the importance and wide prevalence of episodes of intrusive ideas and feelings in states of distress precipitated by serious life events.