A series of 257 cases of carcinoma of the male breast in Denmark has been examined with a view to establishing the factors which might influence the prognosis. Observed and corrected 5-year survival rates of 36% and 46% respectively correspond well with the results in other series. Expressed by corrected survival rate, the prognosis appears to be somewhat more favourable during the period 1958-71 than during the period 1943-57. This improvement of prognosis can be related to a significantly better clinical stage of advancement during the latter period. Comparison of the 5-year corrected survival rates in series of male and female breast cancer shows that the prognosis in male breast cancer is not much worse than the prognosis in females. It has been proved that the duration of disease, the clinical stage and the histological degree of malignancy influence the prognosis considerably. The therapeutic results in our series correspond well with the results found in other series. We did not find any evidence to indicate that it would be better to carry out radical mastectomy than to do simple mastectomy since radical mastectomy has not given consistently better results. It is recommended that treatment of this rather uncommon disease be centralized as far as possible.