A 45-year-old man developed a bloody discharge from his right nipple. Physical examination revealed bloody discharge from his left nipple also but no swelling, breast mass, or axillary lymph nodes. He then underwent bilateral total glandectomy without axillary dissection. Histological examination revealed low-grade ductal carcinoma in situ (DCIS) with a low-papillary and cribriform pattern measuring about 4 mm in diameter in the breast bilaterally. To our knowledge, this is the first report of synchronous bilateral DCIS in a male. Since this patient's hormonal profile showed a relatively high blood level of prolactin, the causative relationship between hyperprolactinemia and male breast cancer is discussed. Including our case, 5 of 6 cases reported thus far have been bilateral, and 4 of the 6 cases have been synchronous. We emphasize that the contralateral breast should also be tested or followed in male breast cancer patients with hyperprolactinemia.