Case histories are reported of 18 patients in whom the diagnosis of primary brain stem haematoma and brain stem haemorrhage was made by computed tomography (CT). The possibility of an early diagnosis of brain stem haematoma, and the differential diagnosis of brain stem haemorrhage by a combination of clinical and tomodensitometric criteria is emphasized. It is concluded that CT is a highly reliable method for the diagnosis, location, and management of brain stem haematoma.