Erdheim-Chester disease is a distinctive pathologic and radiographic entity characterized by bilateral, symmetric sclerosis of the metaphyseal regions of long bones and infiltration of foamy, lipid-laden histiocytes. Clinically, it ranges from an asymptomatic, focal process to a fatal, systemic disease. All previously reported cases of Erdheim-Chester disease are reviewed and a new case with diabetes insipidus, partial hypopituitarism, histiocytic skin lesions, and retro-orbital tumors is presented. An 11-year follow-up reveals progression from a benign, limited process to a progressive, systemic disease. Patients with Erdheim-Chester disease show markedly disparate clinical courses and some features similar to Hand-Schüller-Christian disease. They need careful monitoring and further attempts at treatment.