Sixty-one cases of histologically confirmed solitary intraosseous lipomas were analyzed with respect to clinical, roentgenographic, gross, and histologic features. Two additional cases with multiple intraosseous sites and three additional cases not treated with surgery are also described. Intraosseous lipomas may be subdivided into three groups depending on the degree of involution: I, solid tumors of viable lipocytes; II, transitional cases with partial fat necrosis and focal calcification but also regions of viable lipocytes; and III, late cases in which the fat cells have died with variable degree of cyst formation, calcification, and reactive new bone formation of a characteristic morphology. The tumor is a well-defined entity that may present with varying features due to its stage of evolution. Thus, lipomas have been confused with other benign tumors, cysts, and cases of bone infarction. Intraosseous lipoma is not as rare as the literature suggests, but has been rarely diagnosed. The lesion appears to undergo spontaneous involution, so that surgical excision may not be necessary in some cases.