A series of 27 patients with intramedullary osteogenic sarcomas that were so well-differentiated histologically as to be confused with benign lesions was studied. Of the 27 patients, 14 were females and 13 were males, and most were adults. The tibia and femur were involved commonly. Roentgenographically, the tumors showed a mixture of sclerosis and lysis with poor margination. However, they lacked the highly destructive appearance of high-grade osteosarcomas. Histologically, spindle cells with minimal cytologic atypia were arranged in interlacing bundles. Mitotic figures were scarce. The amount of osteoid was variable, commonly being abundant. With recurrence, three tumors became highly anaplastic. Excision of tumor almost invariably led to recurrences. Resection or amputation has led to good results in seven patients. Only three of the 27 patients died with metastatic tumor; one patient is alive with metastasis. Central low-grade osteosarcomas have been misdiagnosed frequently and hence treated inadequately. Careful roentgenographic and histologic correlation is required to make the diagnosis.