The threefold title, although not entirely satisfactory, has been used, as the lesion has been commonly classified under these terms. Terminology is still in a state of flux, and the author does not have compelling reasons to force the choice of any given term, but he does feel that it is important to recognize the synonymous nature of the various terms already in the literature. The origin of the lesion—that is, whether it arises within or out-side of bone—and the role played by trauma are still matters for discussion. The ability to recognize the somewhat unusual but characteristic features of the lesion is of practical importance, and description of these features has been the purpose of this paper. The tumor differs in many aspects—age of the patients, location, roentgenographic and microscopic appearance—from the genuine giant-cell tumor, and probably represents a reparative process following some as yet undetermined vascular disturbance about the periosteum and surrounding tissues. It seems probable that such a growth might arise from rupture of a periosteal or nutrient vessel with subsequent seepage of blood and tumor formation. Such a hypothesis emphasizes the non-neoplastic nature of the disease and belies any convenient diagnostic term available.