Forty patients with nontumoral epileptogenic lesions who have undergone cortical excision of portions of the frontal lobe for the relief of medically refractory focal epilepsy at the Montreal Neurological Institute during the period 1930-1971 have become and remained seizure free for a minimum period of 5 years (median follow-up 14 years). It seems logical to assume that, in these patients, the essential seizure-producing mechanisms were contained in the excised portions of the frontal lobe and such patients thus represent a pure culture of frontal lobe epilepsy. The clinical, radiological, EEG, surgical, and pathological findings were analyzed. The variability in the clinical pictures and EEG data gives ample testimony of the complex and varied patterns of spread of epileptiform discharges through the brain in patients with epileptiform lesions of the frontal lobe. The data presented also bear on two secondary localizational aspects of frontal lobe epilepsy: (a) how much cortex must be recruited into epileptiform discharge to produce recurring seizures, and (b) how much of the total potentially epileptogenic cortex must be removed to produce a satisfactory reduction of the seizure tendency. These data also emphasize the importance of improving the accuracy of our methods of evaluating these secondary and tertiary localizational aspects of epileptic phenomena.