Primary carcinoma with osteoclast-like giant cells is a very rare tumour of the female breast. The clinical course, histological, immunohistochemical and ultrastructural features of 61 cases of invasive duct carcinoma with osteoclast-like multinucleated giant cells (OMGCs) are reviewed and a new case is presented. The median patient age of all patients included in the review was 42 years, the tumour was located in the upper outer quadrant and the mammographic and gross findings were of a well-defined tumour of dark-brown colour, resembling a metastatic melanoma. Follow-up data in the literature have shown that 86% of patients with these tumours are still alive after 5 years. Histologically, these tumours are invasive ductal carcinomas with OMGCs next to the neoplastic glands and within their lumen. Signs of recent and past haemorrhage are ubiquitously present in the highly vascularized stroma. Immunohistochemical and ultrastructural studies have claimed a benign histiocytic nature of the OMGCs; they may represent a special type of polykaryon, distinct from both osteoclasts and inflammatory giant cells.