Clinicopathological analyses of 6 cases of mantle zone lymphoma (MZL) were carried out. The median age of the patients was 62 years with a range of 41 to 71 years and the male-to-female ratio was 1:1. Superficial lymph node (LN) swelling was present only in 2 patients. Giant LN swellings of the mesenteric or inguinal regions were present in 4, and bone marrow involvement by lymphoma cells in 5. Serum protein electrophoresis revealed a monoclonal protein of IgM kappa type in 2 patients. One of these also had polyclonal hypergammaglobulinemia. An immunohistochemical study of 6 patients revealed LN-1-(-)+, LN-2+(-)++, sIgM+, sIgD+, CALLA +/-(-)+, DRC-1+(-)++. The immunohistochemical features of the cases were similar to those of small lymphocytic lymphoma or follicular lymphoma. Only 1 patients out of 6 achieved complete remission. Two patients died, one of pneumonia after chemotherapy and the other of cancer. The others were alive 4 to 100 months after the diagnoses. Although giant LN swelling and bone marrow involvement of lymphoma cells which were refractory to treatments were frequently observed, we consider MZL to be a slowly progressive and low-grade type of non-Hodgkin's lymphoma.