Here we report two cases of primary skeletal muscle lymphoma. The first patient was an 82-year-old man. On April 2004, he was referred to our hospital because of swelling of the right upper arm. Magnetic resonance imaging (MRI) showed an area which was isointense on T1 and hyperintense on T2-weighted imaging compared with normal skeletal muscle. The size of the tumor was 5 x 7 x 13 cm. Following pathological, flow cytometric and genetic analyses of the specimen, we diagnosed the tumor as a non-Hodgkin lymphoma of the T-cell rich diffuse large B-cell type. The second patient was an 87-year-old man. He was admitted to our hospital on July 2004, under the chief complaint of swelling of the right thigh. MRI revealed a giant tumor mass of the right thigh which was isointense on T1 and hyperintense on T2 imaging. The patient was diagnosed by open biopsy as having diffuse large B-cell lymphoma. We could find only 62 cases of primary skeletal muscle lymphoma through a MEDLINE search. We report on our two cases with a review of the literature.