The solitary osteochondroma, a common pediatric bone tumor, is a cartilage-capped exostosis. Hereditary multiple exostosis is an autosomal dominant disorder manifested by the presence of multiple osteochondromas. Linkage analysis has implicated mutations in the EXT gene family, resulting in an error in the regulation of normal chondrocyte proliferation and maturation that leads to abnormal bone growth. Although exostoses are benign lesions, they are often associated with characteristic progressive skeletal deformities and may cause clinical symptoms. The most common deformities include short stature, limb-length discrepancies, valgus deformities of the knee and ankle, asymmetry of the pectoral and pelvic girdles, bowing of the radius with ulnar deviation of the wrist, and subluxation of the radiocapitellar joint. For certain deformities, surgery can prevent progression and provide correction. Patients with hereditary multiple exostosis have a slight risk of sarcomatous transformation of the cartilaginous portion of the exostosis.