Non-Hodgkin's lymphoma (NHL) is one of the most common malignancies in patients infected with human immunodeficiency virus (HIV): it occurs 25-60 times more frequently in HIV-infected patients than in the general population. This neoplasm in acquired immunodeficiency syndrome (AIDS) patients is a highly aggressive tumour with a poor prognosis and tends to develop in extranodal sites, such as the central nervous system, digestive tract and bone marrow. NHL involving the paranasal sinuses is rare in HIV-infected patients, and is likely to be confused clinically and radiographically with sinusitis; moreover, its optimal treatment is currently uncertain. We present a case of NHL involving the left maxillary sinus in a patient with AIDS. The patient was treated with systemic chemotherapy (low dose-CHOP), but the malignancy did not respond. Subsequently, he was treated with local maxillary sinus irradiation which resulted in partial regression of the neoplasm and in decrease of local symptoms.