Male carcinoma of the breast is not a common clinical problem, but is of interest in the wider context of female as well as male breast cancer etiology. This review discusses recognized and suspected epidemiology associations of male breast cancer, and relates these to potential endocrine factors. It is concluded that altered estrogen production and metabolism, perhaps in part related to body weight in early adulthood, may prove to be the major hormonal involvement in male breast cancer. Future studies should incorporate the more recently developed approaches to investigating estrogen metabolism and bioactivity, and include familial benign and malignant breast disease.