Of the various types of bone neoplasms none, perhaps, have been or are the subject of more interest and discussion among surgeons and pathologists than the so-called giant cell tumors, often referred to as giant cell sarcoma of the epulis type, myeloid sarcoma or osteoclastoma. We have known of this bone lesion for more than eighty years from the work of Lebert1 and, although much study by many capable men has resulted in a general familiarity with its clinical, roentgenologic, pathologic and histologic characteristics, our knowledge of the true nature, behavior and course of the tumors of the giant cell series remains far from complete, and our interpretation of their structure is quite unsatisfactory. Some students, notably Barrie2 and his followers, have regarded the tumor as being a local, chronic, inflammatory process; others feel that it is a true neoplasm. We are not certain of the origin or