Reviewing our experience with 19 cases of male breast cancer, we found two patients with a 12-year history of estrogen therapy for prostatic carcinoma. One initially received diethylstilbene followed by estradiol, 80 mg monthly, and finally estramustin, 140 mg twice daily. The other patient had dienestrol, 2.5 mg daily, and later estradiol, 40 mg every 6 weeks. The possible causal relationship between prolonged estrogen administration and breast cancer in males is in contrast to available epidemiologic data. Therefore, the possibility of an association by chance cannot be ruled out.