Primary lymphoma of bone (PLB) is an extremely rare condition that is usually confused with other primary injuries of the bone. It is characterized by the involvement of one or more bone locations, with or without involvement of regional lymph nodes and viscera. PLB constitutes 3-7% of all malignant bone tumors and approximately 3% of all extranodal lymphomas. It is found at all ages, being most frequently seen in adult life. Any part of the skeleton can be involved, but a trend exists in favor of bones with persistent bone marrow. We report a case of PLB with an unusual presentation: involvement of the proximal phalanx of the thumb. Treatment with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) plus etoposide established complete remission. Consolidation with radiotherapy of the femur and phalanx was performed. There was no evidence of recurrence at the 14 th month follow-up.