Erdheim-Chester disease (ECD) is a rare form of non-Langerhans cell histiocytosis. Herein we describe documented skeletal and pericardial involvement by ECD producing cardiac tamponade in a 30-year-old woman. The diagnosis of ECD was established by histopathology, immunocytochemistry, and by radiologic studies demonstrating diffuse, bilateral, symmetrical osteosclerosis of the long bones, sparing the epiphyses and axial skeleton. Scintography using methyl diphosphonate showed increased uptake in involved bone. The patient presented with jaundice and hepatic congestion produced by cardiac tamponade. Pericardial biopsy revealed xanthogranulomatous lesions comprised of foamy and lipid-laden macrophages, multinucleated giant cells, monocytes, and lymphocytes in a mesh of fibrosis. Immunohistochemical staining was positive for CD68 and negative for CD1a, consistent with ECD rather than with the much more common Langerhans cell form of histiocytosis.