The bone scans of 471 cancer patients revealed 103 (22%) with .gtoreq. 1 rib lesions. Of 69 patients who had serial studies, 5 (7%) had proven rib fractures, 13 (19%) had probable fractures, 25 (36%) had proven metastases, and 26 (38%) had probable metastases. By analyzing the intensity and appearance of rib lesions in serial bone scans, it was concluded that there is a high probability that rib lesions detected by bone scanning are fractures if they are focal as opposed to linear and if they decrease in intensity within 6 mo. or if they are aligned so as to involve .gtoreq. 2 ribs in the same location.