B cell lymphoma arising in skeletal muscle is described with the review of literature. A 72-year-old man visited our hospital on September 21st 1992, because of a right temporal mass which had grown gradually since one year previously. A CT scan and MRI showed a soft tissue mass adjacent to the temporal muscle expanding from the right temporal to infratemporal fossa. Physical examination on admission revealed that the mass at the right temporal region, was non-tender, elastic soft, and 5 x 2 cm in diameter. Some elastic hard masses at the right infraauricular region, approximately 1.5 x 1.2 cm in diameter, were also found. Histological examination of a biopsied specimen obtained from the temporal mass revealed B cell lymphoma, diffuse medium-sized cell type. Tests for surface markers using tumor cell suspension showed positive results for CD5, CD19, CD20, SmIg mu, delta, lambda, but negative for CD10. Chromosomal analysis revealed clonal aberrations, and the defining karyotype as 51, X, +X, -Y, +2, +3, +4, +8, +12. The patient achieved a complete remission after treatment with combination chemotherapy including doxorubicin, cyclophosphamide, vincristine, etoposide, vindesine, procarbazine, and prednisolone.