To quantify the risk of pathologic fracture through the metastatic lesion in a long bone, we used Mirel's scoring system. We checked 4 risk factors from roentgenographic and clinical findings and got a single score by combining those factors. In total 38 cases, we calculated scores through analysis of X-ray films and clinical records before taking radiotheraphy. We used retrospective analysis. We found a mean score 8 in the nonfracture group, where as a mean score 10 in fracture group, we were able to predict impending pathologic fracture by score. There was high risk of pathologic fracture when score is above 9. It is suggested that all metastatic lesions in long bones should be evaluated prior to irradiation. Lesions with scores of 8 or lower can be safely irradiated without risk of fracture, while lesions with scores of 9 or higher require prophylactic internal fixation prior to irradiation.