Abstract: ABSTRACT Erdheim–Chester disease (ECD) is an extremely rare disorder that can affect many different organs of the body. This is an unusual form of non-Langerhans-cell histiocytosis. This is characterized by excessive production and accumulation of histiocytes. The normal function of the histiocytes is to fight infections. Histiocytes accumulate in the loose connective tissue of various organ systems of the body and cause thickening of tissues and may become dense and fibrotic. In the absence of successful treatment, the disease is debilitating and can result in multi-system organ failure. Erdheim–Chester disease is often described in the medical literature as an extremely rare1 entity. Erdheim–Chester disease usually presents in adults aged between 40 and 60 years. Here we present a case report of ECD in a 26-year-old young male patient with progressive course over a period of 4 years with symptoms suggestive of multi-organ involvement. How to cite this article Patil M, Jaiswal D. Erdheim–Chester Disease. J Med Sci 2015;1(3):55-57.