On the basis of our observations, it may be said that bilateral prefrontal lobotomy has proved a useful tool in the treatment of many cases of chronic mental disease where conservative treatment has failed. There is no indication, however, that the operation really cures the patient's disease. Rather it seems to produce a new emotional equilibrium on the basis of which he can function more satisfactorily. This advantage is balanced by certain disadvantageous personality changes. Operation should, therefore, be recommended only when the patient is still capable of emotional reactions, when his thinking is not incoherent, and when the prepsychotic history does not indicate a psychopathic personality. Another important factor is the presence of adequate family resources which would enable the patient to complete his post-lobotomy rehabilitation outside the hospital and provide the necessary guidance in the beginning of a new life in the community.