Clinical results of intraoperative radiotherapy for gastric cancer were reported. One hundred and five cases of gastric cancer were treated by intraoperative radiotherapy. Whatever the stage of the patient was, 3-year survival rate was found to be better in the radiotherapy group than that of the control group (treated surgical resection only). Five year survival rate of the stages III and IV in the radiotherapy group was better than the control group. Unfavorable side effects were observed in 4 cases out of 105 cases. In one case, penetration of postoperative peptic ulcer into the irradiated aortic wall was found by autopsy. Two cases of bile duct stenosis and one case of ileus due to acutely developed peritonitis carcinomatosa were experienced. In conclusion, intraoperative radiotherapy immediately after surgical resection for the treatment of gastric cancer was found to be an effective method. The most effective application of the method appears to be to cases of stage II and III without liver metastasis and peritoneal disseminations (H/sub 0/P/sub 0/, M, A).