Rationale:Primary bone lymphoma (PBL) is a rare malignant entity. There is a better survival of PBL than any other malignant bone tumors and extranodal lymphomas.Patient concerns:We report a rare case of PBL involving radius and tibia. The patient was a 14-year-old girl with left forearm pain and swelling after trauma. Six months later after the last chemotherapy and radiotherapy, pain and swelling of left knee was presented.Diagnoses:Radiological imaging revealed a lytic destruction, periosteal reaction, and pathological fracture of radius and tibia with soft tissue mass. Surgical biopsy was performed, and the result of histopathological diagnosis was diffused large B-cell lymphoma (stage IV, group A).Intervention:Chemotherapy combined with radiotherapy was applied before curation.Lessons:Due to its uncommon presentation, PBL should be taken into consideration if differential diagnosis from other bone tumors is necessary in clinic.