Damage to the frontal lobe is liable to produce personality changes; it is highly probable that lesions have to be bilateral to have this effect. But beyond that, there is little agreement about type, extent and localization within the frontal lobe of the lesions which are followed by personality change. Little is known about the different types of clinical picture caused by bilateral frontal lesions. In a certain proportion of the cases euphoria is the most impressive symptom, and it is for this reason that operations on the frontal lobes have been proposed in the treatment of depressions. (Lit., see Hutton.) The value of the procedure is still under discussion, and its theoretical foundation is far from being understood. This is not surprising, for if one tries to analyse such an operation, one has to take into account at least four variables: the patient's previous personality, his mental illness, the psycho-physiological effect of the lesion, and the psychological effect of operation, nursing care and environmental changes. The cerebral factor is obviously the most interesting one; to judge its importance one tends to interpret the operative results in the light of experience after other frontal operations or injuries.