The primary outcome measure for patients with medically intractable epilepsy is the change in seizure frequency, as measured by the Engel scale before and 1 year after treatment. Secondary outcome measures include 1) percentage of patients who are able to be completely withdrawn from anti-epileptic medication; 2) percentage of patients who are seizure-free (Engel Class I); 3) mean Engel Class one year after surgery stratified by the type of surgical procedure; 4) percentage of patients with permanent neurological side-effects from surgical treatment; 5) incidence of serious complications of epileptic seizures, and 6) neurophysiological correlates of cognitive function. Outcomes for patients with tumor related epilepsy will be assessed under a seperate protocol, 16-N-0041, Tumor Related Epilepsy.