Forty-one patients with multiple cartilaginous exostosis (MCE) were classified into three groups: Group I, no involvement of the distal forearm (n = 8); Group II, involvement of the distal forearm without shortening of the radius or ulna (n = 11); Group III, involvement of the distal forearm with shortening of the radius or ulna (n = 22). Groups were compared with regard to number of lesions, regional morbidity rate, age of onset, height, and presence of valgus deformity of the ankle. From these results, children in Group I were mildly affected. Further, those in Group III were severely affected, and all children in Group III had lesions of the innominate bone or proximal femur, where secondary chondrosarcoma occurs most frequently. This classification should prove useful in estimating severity and identifying cases at high risk for malignant transformation. MCE seemed to be an aberrant enchondral ossification and its mode of development to be reflected in the growth potential of each bone. Dislocation of the radial head occurred in three cases and was the initial symptom in two of these. Dislocation of the radial head may occur earlier than previously thought, hindering its prevention.