The authors present the results with bilateral prefrontal leucotomy in a group of 50 cases of chronic schizophrenia, 3 of mixed psychosis, 9 of chronic epilepsy, 12 of psychopathic personality and 2 cases of perverted postencephalitic syndrome. Out of the schizophrenics, 16% were encouragingly influenced by the operation, the proportion being greater with the paranoical than with the simple forms. The catatonics and the mixed psychoses had no improvement. Seven of the 9 epileptic patients improved as to the personality disturbances, 2 cases being controlled by Mira's myokinetic test. Among the 12 psychopathic patients, only two were benefited (one impulsive, and one paranoic). One of the postencephalitic perverseness cases recovered for 18 months but after this period some of the symptoms returned. The authors agree as to the application of the bilateral prefrontal leucotomy to correct impulsivity and aggressiveness in psychotic, psychopathic and epileptic patients, the results being a beneficial effect on the affective disorders of the personality. The casuistics were summed up in enclosed charts.