1. In this series of schizophrenic patients there was no consistent group change in weight prior to the 6th month after lobotomy.2. At the 6th postoperative month the patients as a group showed a small but significant weight increase. This arose principally from a marked weight gain on the part of a small group of patients.3. The marked weight gains that occurred in certain patients postoperatively led, for the most part, to a resumption of a normal weight rather than to the development of obesity4. Separate analyses of the improved and unimproved groups indicated a trend toward weight gain in the improved patients, and a trend toward weight loss in the unimproved patients.5. The postoperative retraining program did not appear to be responsible for the weight changes after lobotomy.6. These findings indicate an increase in weight does not necessarily follow the operation of prefrontal lobotomy. It is suggested that those patients who do gain weight on a controlled diet do so as a result of the improverd appetite that accompanies amelioration of their mental symptoms. There is no indication from these observations that lobotomy produces any metabolic change leading to abnormal weight increase. The findings instead, would confirm the prevalent belief that obesity following lobotomy results from uncontrolled eating during the postoperative period.