Fifty-four of 103 malignancies of the paranasal sinuses treated at the Cleveland Clinic Foundation between 1977 and 1986 were squamous cell carcinomas. Six arose from the ethmoid sinus and 48 from the maxillary sinus. Of the maxillary sinus patients, 11 presented with T1 or T2 lesions, 20 with T3, 16 with T4, and 7 of these had nodal disease. Treatment was surgery and/or radiation therapy. There was local recurrence in 25 of 48 maxillary sinus patients and in 1 of 6 ethmoid patients. Overall 5-year survival was 38.2% in the maxillary sinus group: T1, 100.0%; T2, 85.7%; T3, 31.8%; and T4, 6.7%. Three of six patients with ethmoid tumors were cured. There was a statistical trend for better prognosis in those patients presenting with ethmoid primaries, with early lesions, treated with both radiation and surgery, and with history of inverting papilloma. There were complications of treatment in 10 patients, four of which resulted in death. Local control was the major problem for these patients; therefore, early detection and aggressive local treatment are desirable.