Erdheim-Chester disease is a rare pathologic entity characterized by symmetrical radiodensities in the metaphyseal and the diaphyseal portions of the long bones. Fibrosis, osteoblastic cortical bone deposition, and fibroxanthomatous granulomas with lipid-laden macrophages and multinucleated giant cells, which have a particular tropism for connective and adipose tissues, are the pathologic hallmarks. To our knowledge, 27 cases have been reported in the literature since the entity was first described in 1930. Protean clinical features range from a focal and asymptomatic process to a multisystemic infiltrative disease. We describe the clinical course of a new case and review the extensive pathologic findings at autopsy, including those demonstrated by light and electron microscopy and cytochemical and immunocytochemical studies.