The computed tomography (CT) scans of 132 patients with late onset epilepsy were compared with the CT scans of an age- and sex-matched control group. Patients with neurologic symptoms in addition to epilepsy, patients with a definite antecedent cause for epilepsy, and patients with tumours on CT scanning were excluded. Fifteen of the patients with epilepsy, as opposed to two of the controls, had infarcts on their CT scans (p = 0.003 Fisher exact test, two-tailed). In nine of these patients only lacunar infarcts were present. No patient had a history of stroke. We concluded that cerebrovascular disease was the major underlying contributory factor to the development of epilepsy in these patients. Twelve of the 15 patients were aged greater than 60 years, representing 21% of the patients in this age group. There was no difference between the epileptic patients and controls in the presence of clinical features of systemic vascular and cardiac disease. CT scan evidence of cerebral atrophy was as common in the control subjects as in the patients with epilepsy.