A bone scan is frequently obtained in patients with breast cancer for evaluation of possible metastatic bone disease or for evaluation of response of known metastases to treatment. These patients commonly wear breast prostheses after unilateral or bilateral mastectomies. On some bone scans, the authors have observed artifacts resulting from certain breast prostheses. In particular, in the patient described, a weighted breast prosthesis was not removed during Tc-99m HMDP bone scanning and was interpreted as being permanent pacemaker or defibrillation unit. The scintigraphic appearance of several commonly used, commercially available weighted breast prostheses is discussed.