Five cases of a rare peculiar type of mammary carcinoma with osteoclast-like stromal giant cells are reported. The tumors are characterized by a large number of multinucleated giant cells in intimate association with the epithelial neoplastic cells. The light and electron microscopic observations confirm the earlier reports about the origin of the giant cells from mononuclear histiocytes as a local response to some tumoral products. In 3 patients a preoperative fine-needle aspiration biopsy was carried out and the cytomorphology of these tumors is described to alert cytopathologists who encounter this entity in the routine breast mass aspiration biopsy.