During the past 15 years, 30 patients with squamous cell carcinomas of the maxillary sinus were treated by modified partial maxillectomy following chemo-and radiotherapy, taking care to preserve facial contour and function as far as possible. Follow-up evaluation showed that local recurrences, and regional lymph node and distant metastases were more frequent in T4 patients than in T3 patients. Evaluation of the histopathological effects of preoperative chemo- and radiotherapy at the time of surgery showed that T4 patients tended to have a poorer response to the treatment than T3 patients. Analysis according to the direction of primary tumor extension showed that the incidence of local recurrence was higher in the superolateral type, whereas that of regional lymph node metastasis was higher in the medial type. The cumulative 5-year survival was high (72.2%) in Stage III patients and low (22.5%) in Stage IV patients. The overall rate was 55.4%. The treatment produced relatively good outcomes in T3 patients but poor outcomes in T4 patients. These findings indicate that T4 carcinoma of the maxillary sinus must be managed initially by a combination of irradiation and multi-chemotherapeutic drugs, and then treated by more extensive surgical resection.