Benign solitary osteochondromas are the most common benign bone tumors and the growth of these tumors occurs by enchondral ossification of proliferative cartilaginous cap, at the junction of cartilaginous cap and bone stalk. Traditionally, it has known that the growth of an osteochondroma stops at about the same time when the parent physis closes. But, some skeletally mature patients had complained gradual growing of exostoses so that we have retrospectively reviewed histological findings of resected 25 benign solitary osteochondromas in priority as well as their radiological findings and records. So, we have had the results as follows:In 6 cases among 13 cases of skeletally mature paients, their exostoses might demonstrate the evidence of growing histologically, becasuse there were enchondral ossification of the proliferative cartilaginous cap without malignant change. In 5 cases among 12 cases of skeletally immature patients, there were involution of cartilaginous cap and no evidence of enchondral ossification, so that the growth of these exostoses might be stopped. So, we concluded that benign solitary osteochondromas might grow beyond skeletal maturity and also cease to grow before skeletal maturity. But further prospective study will be required for the direct evidence of their growth pattern.