A retrospective study of brain investigations of 372 male patients in a maximum-security mental hospital patients is described. All computed tomography (CT) scan and electroencephalography (EEG) reports were collected and rated blind; patients were subsequently divided into 3 groups according to the violence rating of their pre-admission offending behaviour. The 3 groups were similar in their mean age, psychiatric diagnosis, Wechsler Adult Intelligence Scale score and proportions of patients investigated with EEG and CT. In the most violent group, 20% had focal temporal electrical abnormalities on EEG (slowing and/or sharp waves) and 41% had structural abnormalities localised to temporal lobe on CT (dilated temporal horn and/or reduced size of temporal lobe). The corresponding figures for the least violent group are 2.4% and 6.7% respectively. These results suggest that high violence rating scores are associated with temporal lobe abnormalities on CT and abnormal temporal electrical discharges on EEG.