We report a case of intracystic papillary carcinoma of the male breast in a 70-year-old male Caucasian. Grossly, the tumor was a cystic lesion measuring 6 cm in diameter. It contained hemorrhagic fluid and a mural nodule with filiform projections. PAS stain with and without digestion revealed small clumps of diastase-resistant material in the cytoplasm of the neoplastic cells. Grimelius stain was positive. Immunoperoxidase stains were negative for neuron-specific enolase, S100 protein, cromogranin and synaptophysin and were positive for carcinoembryonic antigen and epithelial membrane antigen. On ultrastructural examination the neoplastic cells showed membrane-bound, dense-core secretory granules. We believe that this neoplasm, despite negative neuroendocrine markers, is a variant of mammary adenocarcinoma with endocrine differentiation, partly because of the positive Grimelius stain and partly because of the presence of electron-dense granules, which according to some authors represent lactational differentiation.