Malignant tumours with teratoid or blastomatous features are exceptionally rare in the upper respiratory tract with only 8 documented cases, including the 3 in this report. The tumours occurred in adults aged 27 to 62 yr, and the sites of origin were the ethmoid sinus (4 cases), ethmoid and other paranasal sinuses (2 cases), unspecified sinuses (1 case) and nasopharynx (1 case). The disease was rapidly fatal in 3 cases in which treatment was restricted to surgery and was associated with longer survivals in those given supportive radiotherapy. The tumours are locally aggressive and may invade soft tissues, bone, orbit and cranial cavity. Histologically, the tumours are characterized by a mixture of epithelial and mesenchymal components including cellular elements with immature or embryonal characteristics. These tumours, variously termed malignant teratoma, blastoma, teratocarcinoma or teratoid carcinosarcoma, probably comprise a homogeneous group of neoplasms since their histological and biological features are essentially similar. It is postulated that the tumours develop from primitive embryonic tissues or pluripotential cells that have remained sequestered in the sinonasal tract.