This study examined the longitudinal course, over a 25-month period, of posttraumatic morbidity in a group of 469 firefighters exposed to a bushfire disaster. The patterns of posttraumatic morbidity were defined by the General Health Questionnaire. Contrary to expectation, an acute pattern of morbidity was less common than the delayed-onset or chronic forms. Predisaster variables were found to be as important in the onset and course of the disorder as were the firefighters' losses or extent of exposure to the disaster. These data suggest that exposure to an extreme trauma is necessary but not sufficient to explain the onset and pattern of posttraumatic morbidity.