Erdheim-Chester disease is a rare, non-Langerhans cell form of histiocytosis characterized by osteosclerosis of the metaphyseal regions of long bones, diabetes insipidus, proptosis, and retroperitoneal fibrosis. The latter usually involves the perirenal area and leads to hydronephrosis. Periaortic fibrosis is less frequent. We describe 3 unusual cases of Erdheim-Chester disease with periaortic fibrosis involving the whole aorta and leading to a "coated aorta" appearance on computed tomography scans. Faced with such a singular "coated aorta," bone scintigraphy can be very helpful when searching for Erdheim-Chester disease.