Technetium-99m-methylene diphosphonate (Tc-99m MDP) scintimammography (SMB) was used to investigate palpable breast masses during routine presurgical bone scintigraphy, for women at high risk for cancer and who were candidates for surgery or excisional biopsy. Upright anterior and prone lateral views of the breasts were acquired from 65 women with palpable breast masses, 5-10 min after intravenous injection of 740 MBq of Tc-99m MDP. Breast cancer was histologically diagnosed in 50 women (77%) and benign disease was found in 15 women (23%). Of these 50 breast cancer patients, 44 (88%) showed abnormal MDP uptake in breasts. Among the 15 cases of benign lesions, only 1 (7%) showed abnormal MDP uptake in the breasts. The diagnostic sensitivity, specificity, and accuracy were 88%, 93%, and 89%, respectively, for the differentiation of malignant and benign breast masses. Scintimammography with Tc-99m MDP is a useful and cost-effective tool for differentiating malignant breast masses from benign breast masses.