From a series of 255 patients who had undergone temporal lobectomy for the relief of intractable psychomotor epilepsy, all 47 patients with 'alien tissue' (small tumours, hamartomas, focal dysplasia) in the resected temporal lobe were contrasted with a group of 41 patients who showed mesial temporal sclerosis in their resected lobe. Five per cent of the mesial temporal sclerosis group and 23% of the alien tissue group were psychotic. A marked interaction occurred between psychosis and 'left handedness'. In the alien tissue group, females, especially left-handed females, were the most likely to have developed a schizophrenia-like psychosis.