[MIM*133700] a disturbance of endochondral bone growth in which multiple, generally benign osteochondromas of long bones appear during childhood, commonly with shortening of the radius and fibula; the skull is not involved; the ill effects are usually mechanical but malignant change is rare; autosomal dominant inheritance with genetic heterogeneity. Type I is caused by a mutation in the exostosis-1 gene (EXT1) on 8q, type II is due to mutation in the exostosis-2 gene (EXT2) and type III maps to 19p. SYN: hereditary deforming chondrodystrophy (1), multiple exostosis, osteochondromatosis.