1. Complete lobotomy causes too much blunting of the personality to warrant its further use except in severely deteriorated psychotic patients.2. Selective cortical undercutting is presented as a new method of fractional lobotomy and offers certain technical advantages over other methods, in precision, preservation of adjacent blood supply, facility, and accessibility.3. A sufficient number of undercuttings have now been done to permit specific recommendations for its therapeutic use.4. The results of undercutting indicate that there is little specificity of the frontal lobes in their effect on psychoses but definite specificity in their effect on personality. The psychoses are favorably affected by quantitative isolation of any area of the frontal lobes. The personality is unaffected and shows little if any blunting following isolating of the orbital surface and a definite blunting upon isolation of the superior surface, similar but to a less degree to that found in a standard lobotomy.5. There is more apparent personality deficit in nonpsychotic than in psychotic patients following any type of lobotomy. Hence only fractional lobotomies should be used in patients suffering from mood disorders, neuroses, or pain.6. Undercutting of the orbital surface appears the ideal operation for psychoneuroses and milder mood disturbances because of the almost complete absence of personality change.7. Undercutting of the superior surface or the orbital surface is recommended for the schizophrenic and severe affective psychoses, the results being roughly equal to those obtained in standard lobotomy with significantly less personality deficit.8. Pain, if accompanied by addiction, psychalgia, or excessive anxiety, responds well to undercutting of the superior surface.9. Undercutting of the medial, cingulate gyrus surface is technically more difficult and dangerous with inferior early, and possibly equal late, results making final evaluation difficult.10. Certain cases showing an inadequate response to selective undercutting can be converted to a more complete lobotomy as a second-stage procedure.