Data on 50 patients treated surgically for intractable focal epilepsy were analysed. There were 10 hemispherectomies, 32 temporal lobectomies and eight operations to other areas of the brain. The median age at operation was 14 years. 29 patients were found to have mesial temporal sclerosis or sclerotic hemispheres and 17 had alien tissue and one sclerosis with heterotopia. No lesion was found in three cases. The nature of the first seizure was found to relate significantly to pathology. 30 patients had suffered an early convulsion. Between the convulsive insult and the onset of focal epilepsy there was a silent interval, the duration of which was biased by sex and side of lesion. The remaining 20 patients, of whom a highly significant number had alien tissue, had not had an early convulsion before the onset of focal epilepsy. The importance of accurate clinical histories is stressed. Clinical considerations alone predicted the pathology and laterality of the lesion in more than half the series. Regular EEG recordings and repeat scanning were found to be important investigations. Major disorders of behaviour had occurred in 44 patients. As adults, the series were free of severe psychiatric symptoms, but many required years of careful rehabilitation. 31 children had been excluded from normal schools before operation. Postoperatively, many patients continued their education in normal schools. Some required basic remedial teaching, others successfully undertook higher education and training. 49 patients benefited over-all from neurosurgical treatment. 34 had no more habitual epilepsy at all. Full global gains often took at least five years to achieve.