Erdheim-Chester syndrome is a rare multisystem disease in which progressive xanthogranulomatous infiltration of several tissues are seen. Knee and leg pain are the most common symptoms and bilateral symmetric sclerosis of metaphyseal region of long bones of the lower extremity is typical. Histologically, it resembles Langerhans cell histiocytosis (LCH). However, it is still a matter of discussion whether Erdheim-Chester syndrome is a distinct entity or a type of LCH. The present case is a 46-yr-old man, that presented with signs and symptoms of diabetes insipidus and hypogonadotropic hypogonadism simultaneously. X-rays and bone scintigraphy showed typical and pathogonomic findings of Erdheim-Chester syndrome. Bone biopsy and immunohistochemical staining strongly support the diagnosis of non-Langerhans cell histiocytosis.