A preliminary analysis of the effectiveness of intraoperative radiotherapy with an electron beam for the treatment of prostatic cancer in 14 patients is presented. The perineal approach was employed as an operative procedure for placing a treatment cone onto the tumor. The electron energy used for irradiation ranged from 10 to 14 MeV. Of five patients treated by intraoperative radiotherapy alone, four who received single doses of 3000 to 3500 cGy achieved local control. One of these patients, however, who received 3000 cGy, had a local recurrence occurred at the sixth year after the treatment. A patient treated with 2800 cGy failed. A single dose of 2000 or 2500 cGy was delivered intraoperatively to nine patients as a boost dose in conjunction with external irradiation of 5000 cGy for the treatment of pelvic lymph nodes. All nine patients achieved local control. None of the 14 patients developed any serious complication of the bladder, urethra or rectum, which has been associated with intraoperative electron irradiation. Although no definite conclusion can be drawn at present because of the small number of patients and insufficient follow-up, the results suggest that single doses of 3300 cGy by intraoperative radiotherapy alone or 2500 cGy as a boost in conjunction with external radiotherapy can be curative for prostatic cancer with minimal morbidity.