Many cases of familial aggregation of lymphoproliferative malignancy have been reported. But familial aggregation of non-Hodgkin lymphoma is less frequent than Hodgkin's disease, Burkitt's lymphoma, and adult T-cell leukemia. Here we report familial B-cell lymphomas occurring in a mother and her daughter at the same time. The daughter (43 years old) was admitted because of fever. She died of a rapidly progressive neurological disturbance. The mother (75 years old) was admitted because of fever and pleural effusion, and then died with a complication of cryoglobulinemia. The histological findings of their lymph nodes revealed diffuse lymphoma, medium-sized cell type, with B-cell phenotype and mixture of cleaved and non-cleaved nuclei. They had no common chromosome abnormalities, while they shared HLA-A 2, B 35, and Cw 3 antigen. Viral infection was not identified, by routine serological test and electronmicroscopic study.