The occurrence of breast cancer in aged male and his paternal uncle is reported. A review of previously reported cases of male breast cancer (M.B.C.) occurring in families and the association with other cancers in the family members is included. Familial or hereditary factors have not been recognized as a major contributing factor in previous reports. Seven families (63.6%) out of eleven families reported had females with breast cancer. It appears that there are some families in which males as well as females have increased risk of developing breast cancer. It is believed that this report supports the genetic predisposition of breast cancer in males. Estrogen affects the growth of breast cancer through estrogen receptor. An approach to subsequent genetic studies of breast cancer may be to focus on steroid hormone receptors.