This report is a retrospective study of 20 histologically proven malignant maxillary sinus cancer patients treated in the Dept. of Tumor clinic, Presbyterian Medical Center from Apr. 1982 to Aug. 1990. CT in an excellent imaging modality to asses accurately the extent of malignant maxillary carcinoma. The results were as follows: 1. The average age of the patients was 52.3 years old. 2. Histologically, the cancers were composed of epidermoid carcinoma, rhabdomyosarcoma, osteosarcoma, adenoidcystic carcinoma, adenocarcinoma and undifferentiated carcinoma. 3. All cases are advanced in instage. 4. CT findings of mixillary sinus cancer were soft tissue density filling the maxillary antrum, soft tissue dunsity beyond the antrum, low density within the mass, punctate or amorphous calcifications within the mass, antral expansion and irregular bony wall thickeness, maxillary bony wall destruction, lymphadenopathy and distant metastasis. 5. Destruction of surfaces of maxillary bony walls were seen in the nasal surface(20 cases), facial surface(16 cases), intratemporal surface(14 cases) and orbital surface(11 cases). 6. The superioty of CT 개 the conventional sinus radiologic imaging were evident in different are as of tumor evaluation of tumor invasion to the infratemporal fossa, posterior ethmoid sinus, orbital apex, nasopharynx, cribriform plate, sphenoid sinus and skull base. 7. The limitations of CT in evaluation of maxillary sinus was evident in woys, poor differentiation between pooled secretion within the obstructed sinuses and tumor, and determination of invasion of soft tissue structures.