The role of scintimammography with 99mTc-MDP was investigated in patients with mammographic or clinical evidence of breast lesions, suspicious for malignancy, in our Department at the National Cancer Institute of Naples. The end-point of the study was to assess the uselfulness of this test in diagnosing or ruling out breast cancer in more than 2000 women. Scintimammography results were compared with those of mammography and ultrasound and categorized according to histological findings. Overall sensitivity was 92%, specificity was 90%, and accuracy 91%. Sensitivity was affected by the lesions exceeding 12 mm and specificity by sclerotic and/or hyaline or myxoid fibroadenomas, which may be positive. The major advantages of scintimammography appeared in the study of calcifications without a mass and of the indirect mammographic signs of breast cancer, such as distortion and asymmetry. Scintimammography with 99mTc-MDP is a reliable, safe and highly cost-effective procedure to diagnose or to rule out breast cancer, after mammography and ultrasound have yielded questionable results.