A case of clear cell chondrosarcoma of the rib in a 30-year-old man is described. The tumor developed at the site of repetitive low-impact trauma (on the arm of a wheelchair) over a period of 24 years. An association between chondrosarcoma and external trauma has not been previously reported. Chondrosarcoma has been described in previously irradiated bone and in Paget's disease. In both these examples there is an increase in new bone formation associated with necrosis of bone and increased resorption of bone, respectively. A possible mechanism in our case is increased new bone formation elicited by repeated microfractures of trabeculae of rib bone.