In order to determine the factors influencing outcome following craniotomy for trauma in patients over the age of 65 and to establish criteria for surgical intervention, the authors carried out a retrospective analysis of the hospital and general practice records of all head injury patients over the age of 65 who underwent a craniotomy for evacuation of a post-traumatic haematoma within 7 days of injury at Frenchay Hospital during a 10-year period (1980-89). Outcome was measured using the Glasgow Outcome Scale and patients were allotted to a good outcome group (good recovery or moderate disability but independent) or a poor outcome group (severe disability, vegetative state of death). There were 35 men and 31 women with a mean age of 72.5 years (range 65-85 years). The mortality rate was 61% and 9% of patients survived in a severely disabled or vegetative state. All 20 (30%) patients with a good outcome had a Glasgow Coma Score (GCS) of 5 or more immediately before surgery. All 18 (27%) patients with a GCS of 4 or less and all 22 (33%) patients with unilateral or bilateral pupillary dilatation had a poor outcome. Outcome was significantly worse in the older patients (75-85 years) compared with the younger patients (65-74 years) and in those patients requiring craniotomy within 24 hours of injury, but the mechanism of injury (fall or road traffic accident), the presence or absence of skull fractures and limb fractures and the pre-operative CT scan appearances did not influence outcome. This study confirms the high probability of poor outcome following surgical evacuation of traumatic intracranial haematomas for elderly head-injured patients with pupillary dilatation or extensor motor responses. Craniotomy under these circumstances is not justified.