From 1975 through 1988, nine patients with locally confined nasal non-Hodgkin's lymphoma (NHL) were treated with radiation therapy in the Department of Radiology, Chiba University Hospital. Immunohistochemical study disclosed that all NHL's have T-lineage. Additionally, unique histological pictures of polymorphism, angiodestruction, and necrosis were seen in most of cases. These three findings are the histological features of polymorphic reticulosis (PMR), which is the main cause of lethal midline granuloma and has recently been shown to belong to T-cell malignancy. Therefore, it is concluded that the nasal T-cell NHL and PMR are really a single disease entity. The predominance of the T-cell lymphoma in the nasal cavity as well as its histological distinctness clearly indicate that the head and neck extranodal NHL cannot be discussed together. Although the disorder was considered to be locally limited at presentation, only 3 of the 9 patients with nasal NHL could be induced into long-term remission with involved field radiotherapy. The distant extranodal spread was the primary cause of failure. Multimodality treatment using intensive chemotherapy might improve the prognosis of nasal NHL.