A retrospective study has been undertaken of 104 men with breast cancer, all of them having a follow-up period of at least 5 years. In 78 cases a histological diagnosis was obtained. The preferred treatment for operable cases was radical mastectomy, in which 60 per cent positive axillary nodes were found. Five-year survival is 54 per cent and the disease-free interval is 42 per cent. Local recurrence occurred in 26 per cent and 16 per cent had developed distant metastases. The overall results are similar to those in the literature with the exception of those for stage III who did better in this series. The generally held beliefs that Klinefelter's syndrome is the strongest predisposing factor to developing male breast cancer and that gynaecomastia is not a premalignant condition are supported by this study. Comparison of results from this series, with those of women of the same age having breast cancer leads to the conclusion that the prognosis in male breast cancer is no worse than for women with comparable disease.