While the treatment of children with Type I diabetes mellitus has dramatically improved since the introduction of insulin in 1922, significant acute mortality still remains. To better ascertain the causes of death in younger children and adolescents with diabetes mellitus, a retrospective review was undertaken of diabetes associated mortality in the patient population followed at the Children's Hospital of Pittsburgh between the years 1950 and 1985. Fifty-five deaths were identified of which 20 occurred during the initial presentation of diabetes and 35 occurred between 2 months and 11 years following the diagnosis of diabetes mellitus. Diabetic ketoacidosis (DKA) was associated with 64% of the total mortality with 85% of the early onset and 54% of the late onset deaths being ketoacidosis related. Of these ketoacidosis associated deaths, cerebral edema was documented in 31%, or 20% of the total group mortality. Non ketoacidosis deaths in both early and late onset groups were caused by heterogeneous events. There were no deaths associated with the traditional late vascular complications of diabetes mellitus. Since diabetic ketoacidosis is a potentially preventable acute complication of diabetes mellitus and represented a predominant cause of mortality in these children, early recognition and prompt treatment might substantially reduce childhood mortality in patients with Type I diabetes mellitus.