Primary radiation therapy for clinically localized prostatic cancer is effective and safe. Of our 147 patients treated between 1964 and 1973, 144 were evaluated 5 years after the initial date of radiation therapy. At 5 years the over-all survival rate was 80 per cent and the rate of survival free of disease was 63 per cent. More than 70 per cent of the patients were free of progression 5 years after the date of the first radiation treatment. Analysis revealed a highly significant association between tumor grade and patient survival (p less than 0.001), and between tumor grade and the interval free of disease (p less than 0.002). The relationship between tumor stage and time to progression of disease also was significant (p approximately equal to 0.01) but there was no relationship between lower stage and longer survival. Of the 142 patients who completed treatment only 20 (14 per cent) had local recurrence of the prostatic cancer after radiation therapy, representing a local control rate of 86 per cent 5 years after treatment. A few of the patients underwent post-treatment prostatic biopsy after radiation therapy. If a biopsy is done for increased prostatic induration and the results are positive adjuvant treatment is recommended. In the absence of urologic symptoms of progressive induration of the prostate gland biopsy is not instrumental in predicting the course of the cancer.