Fifteen patients have been followed for more than one year following callosotomy having presented with long standing epilepsy, no well defined focus amenable to radical excision, and severely incapacitating atonic seizures that were refractory to anticonvulsant therapy. Atonic fits have been reduced by more than 80% in thirteen patients, with two patients suffering long term sequelae (slight dysarthria in one, and dyslexia with mild visuo-spatial disturbances in another). Anticonvulsant therapy was still required post-operatively.