PURPOSE: To compare the feasibility of 9 9 mTc-MIBI scintimammography as a tumor localizing agent in breast lesions in comparison with that of mammography and ultrasonography, and to evaluate the efficacy of these three modalities. MATERIALS AND METHODS: Sixty-four breast lesions were classified as benign or malignant on the basis of sono-graphic and mammographic criteria and were further analyzed by means of 99mTc-MIBI scintimammography. The classifications thus obtained were compared with the biopsy findings, and in order to compare the three techniques, the sensitivity, specificity, accuracy, and negative and positive predictive values were calculated for each individual modality. RESULTS: Of 64 histologically proven lesions, 33 were malignant and 31 were benign. Sensitivities and specificities for malignancy were 86.2% and 64.5% for mammography, 87.9% and 76.7 % for sonography, and 78.8% and 74.2% for 99mTc-MIBI scintimammography. CONCLUSION: Mammography and ultrasonogrphy are reliable diagnostic modalities for the detection of breast cancer. 99mTc-MIBI scintimammography has a higher specificity than mammography and it may help to reduce unnecessary biopsies.