In a 57-year-old woman dizziness, staggering, altered mental status, and bilateral pain and cramping in the lower extremities developed. Extensive investigation yielded evidence of renal and long-bone lesions, with the latter being primarily metaphyseal and diaphyseal. Needle biopsy of the tibial marrow revealed the presence of lipid-laden histiocytes, osteosclerosis, and osteoclasts. A diagnosis of Erdheim-Chester disease was made; this is the 16th known case of the disease. The patient responded well to steroid therapy but later was readmitted and ultimately died of extensive infiltrates in the kidneys and pancreas. Erdheim-Chester disease, an extremely rare multisystem histiocytic disorder, has been characterized as a lipid (cholesterol) granulomatosis. Renal, cardiac, and pulmonary involvement are noted in most cases; the roentgenographic signs of skeletal involvement, when present, are pathognomonic.