The underlying seizure tendency of complex partial seizures often involves the temporal region of the brain, but the frontal lobe can also produce similar complex partial seizures. By the end of 1980, 1,210 patients with medically refractory temporal lobe epilepsy had been operated on at the Montreal Neurological Institute. Nontumoral epileptogenic lesions were present in 1,034 patients, 169 had tumors, and 7 had major vascular malformations. Thirty-seven percent of the 894 evaluable patients with nontumoral epileptogenic lesions have become and remained seizure-free. Two hundred thirty-six (26%) patients had a marked reduction of seizure tendency. Within the seizure-free group, 63% had a complete or nearly complete reduction of their medically refractory tendency following temporal lobectomy. Of the patients with temporal lobe epilepsy due to tumoral lesions, 46% of the evaluable patients have become and remained seizure-free, and 76% have had a complete or nearly complete reduction of seizure tendency.