Carcinosarcoma of the breast is a rare, biphasic, tumour with epithelium and mesenchymal components. Its histogenesis is controversial and, hence, has received various different nomenclatures. At present, all studies indicate that it is a variety of methaplasic tumour and suggest multi-potential myoepithelial cell origin. Clinically, it presents as a tumour of variable size and its diagnosis has been by immunohistochemistry studies, or by electron microscopy. We present, here, a patient with mammary carcinosarcoma a difficult diagnosis. Treatment for the patient was a modified radical mastectomy, and adjuvant therapy.