Multiple osteochondromas (MO) is characterised by development of two or more cartilage capped bony outgrowths (osteochondromas) of the long bones. The disease is Multiple osteochondromas (Orphanet_321, an Orphanet rare-disease nomenclature term). Also known as: Bessel-Hagen disease, exostoses, multiple, hereditary multiple osteochondromas, multiple cartilaginous exostoses, multiple congenital exostosis, multiple exostosis syndromes, multiple ostechondromas, osteochondromatosis syndrome.