Primary non-Hodgkin's lymphoma of the liver is very uncommon, and fewer than 100 cases have been reported in the literature. Most reports describe either solitary or multiple mass lesions in the liver. A diffuse lesion without nodule formation is a relatively rare form of the disease. The histologic feature of the disease is a predominantly large cell lymphoma of B-cell lineage. We report a case of primary B-cell non-Hodgkin's lymphoma which had diffusely infiltrated the liver without nodule formation.