Of 572 patients with prostatic carcinoma, 497 received endocrine therapy as the initial treatment. These patients were surveyed in a cooperative research study by members from five universities. Prognosis, causes of death and side effects of estrogen therapy were studied. The prognosis of patients who had received endocrine therapy became worse, as the stage progressed. The prognosis of those who had received a combination of estrogen therapy with castration tended to be better than that of those who had received estrogen therapy alone. Similarly, the prognosis of those who had received a combination of progesterone therapy with castration tended to be better than that of those who had had progesterone therapy alone. No relationship was found between estrogen doses (low, medium and high) and prognosis, although a precise comparison among the three could not be made because of the smaller number of patents with low doses. A high dose of estrogen may not always be the indication, rather a medium dose such as 300 mg diethylstilbestrol diphosphate may be clinically appropriate. The cause of death could be identified in 303 patients who had received endocrine therapy. Cancer-related death was the most frequent (63.7%), and cardio- or cerebrovascular death accounted for only 14.2% of the cases. When this analysis was confined to the patients who had received estrogen therapy, estrogen administration seemed to be the cause of cardio- or cerebrovascular death of 16.1% of the patients. Daily dosing of estrogen was not definitely related to the incidence, or the interval to cardio- or cerebrovascular death. However, among the patients who had died of cardio- or cerebrovascular disease, 50% of the patients who had received a medium or high dose of estrogen tended to die within two years after treatment, while 50% of those who had received a low dose died within three years.