The case of a man who died from the effect of strontium-concentrating metastatic tumor of the lung fields is reported. The origin of these tumors was osteosarcoma in the mid-shaft of the left tibia bounded at either end by a benign cartilaginous tumor. It was also discovered that the patient had had an asymptomatic lesion of this tibial area four-and-one-half years prior to his death and it would seem highly unlikely that the osteosarcoma had been present throughout the entire course of the benign cartilaginous lesion. Although tissue from the lung was not available for histological examination, the uptake of radioactive strontium indicates active osteogenesis in the metastatic nodules. This case is presented as an osteosarcoma taking origin in a solitary, benign enchondroma of a long bone in a middle-aged man.