A case of pure neuroendocrine carcinoma of the breast occurring in a 51-year-old female is described. The tumor located in the upper outer quadrant was a relatively well-circumscribed, uncapsulated, yellowish white, rubbery mass measuring 2.5×2.0×2.0 cm. Microscopically, the tumor was characterized by solid nest, lobular, trabecular, and insular arrangements of small to medium-sized cells with uniform round to oval hyperchromatic nuclei and pale to eosinophilic cytoplasm. It showed focal stromal invasion. The stroma was fibrous and rich in vascularity. The tumor cells were argyrophilic and positive for cytokeratin CAM5.2, Leu-7, neuron-specific enolase, and chromogranin A. Electron microscopy showed neurosecretory granules. The tumor was DNA diploid with a low S-phase fraction by flow cytometry. The axillary lymph nodes were negative for metastasis. The patient was well and without disease 16 months after mastectomy.