Forty-one patients with adenocarcinoma of the prostate localized in the pelvis (stage A2, NX; 3, A2, pN0; 5, B, NX; 5, B, pN0; 1, C, NX; 13, C, pN0; 7, C, pN1; 7) underwent curative external radiotherapy. Thirty-two cases were treated by fast neutron combined with or without Liniac X-ray and 9 cases were treated by Liniac X-ray. Twenty-six cases were well controlled by radiotherapy, but 15 cases recurred and were followed by endocrine therapy. The types of recurrence were local growth in 3, distant metastases in 11, and both in 1. These recurrences occurred in the cases of large prostatic carcinoma, small radiation field in NX cases or low radiation dose. The five-year disease-free survival rates of stage A2, B, C were 86, 66, and 47%, respectively and the five-year overall survival rates were 100, 100, and 53%, respectively. The cases with well differentiated carcinoma had better prognosis than those with poorly differentiated carcinoma (p less than 0.05). As 58% of the cases which were given concomitant endocrine therapy were controlled for over 2 years, endocrine therapy seems to be effective in the cases of failure after radiotherapy. Most of the complications were slight and only one case with complication of sacral decubitus needed surgical treatment. It was concluded that external radiotherapy was a good modality for prostatic carcinoma localized in the pelvis.