Polymorphic reticulosis, Wegener's granulomatosis, and idiopathic midline destructive disease have been known as a lethal midline granuloma. However, recent investigations propose that the polymorphic reticulosis might be a variant of malignant lymphoma and could be originated from B cells, T-cell or histiocytes. The clinical features of 24 pathologically diagnosed polymorphic reticulosis patients were reviewed. To clarify the cell origin of polymorphic reticulosis, 14 cases were studied immunohistochemically using monoclonal antibodies for T-cell and B-cell subsets(MT1, MT2, MB1, MB2, Clonab Co.). Among the 24 cases, the lesions were found in the nasal cavities in 14 cases, 4 cases in palatine tonsils, and 4 cases in soft palates repectively. 20 patients were clinically followed-up : 7 patients received combined treatment with radiation therapy and systemic steroid, and 12 patients took radiation therapy only, and 1 patient took radiation therapy after Denker's operation. Among 20 patients, 10 patients were died of polymorphic reticulosis. The common causes of death were chronic renal failure, lower G-I bleeding, and hepatic failure which may be due to metastases. In the immunohistochemical study, 12 cases out of 14 were postive for MT1 and negative for MB2 and MT2. The expression for MB1 was variable. Among two cases which were negative for MT1, one case showed positive for MB2 and the other showed negative reaction for MB2. These results are highly suggestive that the majority of polymorphic reticulosis are probably a kind of T-cell lymphoma. Therefore, the evaluation for distant metastasis at the time of diagnosis is mandatory, and the polymorphic reticulosis should be considered to be treated with the same or similar regimen using in malignant lymphoma.