A six-year-old boy developed symptomatic cerebral swelling four hours after the initiation of treatment for newly diagnosed diabetes mellitus complicated by ketoacidosis. Ventriculostomy documented intracranial pressure over a two-day period. Increased intracranial pressure unresponsive to controlled hyperventilation and sedation was treated by administering a diuretic and by drainage via a ventriculostomy. Intracranial pressure monitoring was a useful adjunct in management of this rare, but often lethal, complication of diabetes mellitus. One year later, both school performance and the results of a neurologic examination were normal.