Clinical records and radiographs of 203 female patients with 516 metastatic breast lesions located in the proximal femur were examined retrospectively to determine: the dimensions of those lesions that were at risk of fracture; and the relationship of other variables (bone pain, body habitus, age, and radiation treatment) with the occurrence of a pathologic fracture. Twenty-three patients sustained 26 pathologic fractures. Their average age, height, and weight were not significantly different from the 180 patients without fractures. Similarly, moderate to severe bone pain was experienced by a great majority of the total patient population, yet only 11% sustained fractures. Fifty-six patients received radiation treatment of a femoral metastasis. Ten of these patients subsequently sustained fractures. Radiation treatment relieved bone pain but did not have any consistent curative effect on the lesion itself. Finally, the authors were unable to identify either a specific percent involvement of the bone or a critical diameter for metastases that fractured because: 296 (57%) of the 516 metastases were permeative lesions and unmeasurable; 14 (54%) of the 26 pathologic fractures observed occurred through unmeasurable lesions; and the 12 measurable lesions that fractured had the same range of percent involvement as the 208 measurable lesions that did not fracture. Breast metastases at risk of fracture cannot be identified by measurements obtained from standard radiographs alone.