Multiple diffuse fibrosarcoma of bone is a very rare condition, with only 3 cases reported. Its presentation is like that of a multiple myeloma or a metastatic tumor, with multiple osteolytic lesions, and its extent is limited to the bones. Disseminated involvement of the vertebrae was detected in a 26-year-old man, suggesting a metastatic tumor; however, no primary organ or soft-tissue mass was identified. The histopathologic findings of the biopsy material were consistent with fibrosarcoma. Despite treatment, the patient died within 15 months.