In 1990, a 50 year-old man was referred to us for hyperprolactinemia. At 37 years of age the patient had undergone left mastectomy, for a histologically confirmed gynecomastia and, in 1989, he had undergone pituitary adenomectomy, for a PRL secreting macroadenoma (PRL = 3520 ng/ml). Persistently high PRL plasma levels (PRL = 550 ng/ml) showed an incomplete surgical removal of the adenoma and as a consequence, radiotherapy of the pituitary area was performed in 1990. When the patient referred to us, PRL plasma levels were still pathologic and medical therapy with bromocriptine was started. A year later a replacement therapy with cortisone, testosterone, L-thyroxine, was commenced, as the patient presented a post-radiotherapy hypopituitarism. Since the treatment with bromocriptine was unsuccessful, the drug was replaced with cabergoline, but not even the latter was able to normalize PRL plasma levels. In 1996, a nodule of 3 cm in diameter was discovered under his right mammary areola. The nodule biopsy showed a grade II infiltrating ductal breast carcinoma positive to the estrogen and progesterone receptors analysis. A right total mastectomy was performed and the diagnosis was confirmed through histological examination. A case of gynecomastia and breast cancer in a male patient who had been exposed to high PRL plasma levels for several years is reported. In this patient, both elevated PRL plasma levels and a relative hyperestrogenic state may have contributed to originate breast cancer.