Abstract Results of a retrospective study of 397 patients with focal seizures, evaluated by computed tomography (CT), reveal the important role of CT in establishing an etiologic diagnosis. One hundred eighty-two patients (46%) had abnormal scans. The most common lesion was a slowly growing tumor which was identified in 46 patients (11.6%). Other abnormalities demonstrated included generalized and focal atrophy, infarctions, infections, arteriovenous malformations, porencephalic cysts, tuberous sclerosis and leukodystrophies. Sixteen percent of the lesions demonstrated by CT were amenable to corrective surgery.