Diabetes insipidus (DI) is an uncommon but important complication in the head-injured population. A retrospective review of all trauma patients admitted to the intensive care unit (ICU) during a 4-year period who developed DI was undertaken. The incidence of DI was 1.3 per cent in ICU trauma admissions and 2.9 per cent in traumatic head injuries admitted to the ICU. The overall mortality was 69 per cent (18/26). The mean onset time of DI in nonsurvivors (1.5 +/- 0.7 days) was shorter compared to survivors (8.9 +/- 10.2 days) (P < 0.001). All patients who died developed DI within the first 3 days of hospitalization. Patients who develop DI early in their course have a higher mortality than those who develop DI later in their hospital course. The development of diabetes insipidus after head injury carries a 69 per cent mortality rate, and if the onset is within the first 3 days after injury, mortality rate rises to 86 per cent.