A weighted scoring system is proposed to quantify the risk of sustaining a pathologic fracture through a metastatic lesion in a long bone. This system objectively analyzes and combines four roentgenographic and clinical risk factors into a single score. Retrospective analysis of metastatic long bone lesions was completed in 78 lesions that had been irradiated without prophylactic surgical fixation. Clinical data and roentgenograms were scored prior to irradiation by independent observers. The outcome identified 51 lesions that did not fracture during the subsequent six months and 27 lesions that fractured within six months. A mean score of 7 was found in the nonfracture group, whereas the fracture group had a mean score of 10. The percentage risk of a lesion sustaining a pathologic fracture could be predicted for any given score. As the score increased above 7, so did the percentage risk of fracture. It is suggested that all metastatic lesions in long bones be evaluated prior to irradiation. Lesions with scores of 7 or lower can be safely irradiated without risk of fracture, while lesions with scores of 8 or higher require prophylactic internal fixation prior to irradiation.