Primary non-Hodgkin's lymphoma of the maxillary sinus is a rare lesion. We studied nine patients with malignant lymphoma involving the maxillary sinus, treated between 1980 and 1994 in the Kyushu University Hospital. All lymphomas had a diffuse pattern; five were the large-cell type, two the mixed type, and one the small lymphatic and small cleaved type. Immunohistologically, all tumors were B-cell type. Using the Ann Arbor staging system, six patients were classified as stage I, two stage II, and one stage IV. Two patients received only radiotherapy because of advanced age; the remaining seven received a combination of radiotherapy and chemotherapy (CHOP or VEPA). The tumor doses ranged from 30 to 51 Gy (mean, 46.7). The mean follow-up was 51 months. Only one patient (stage IV) died of disease, and eight stage I-II patients were rendered disease-free. The 5-year survival rate was 80%, suggesting that primary lymphoma of the maxillary sinus has a relatively good prognosis.