PURPOSE: To assess the diagnostic usefulness of multimodality study in the diagnosis of breast cancer. MATERIALS AND METHODS: Eighty-one patients between January 1998 to December 1999 were involved in this study, and who underwent mammography, breast ultrasonography, and 99mTc-MIBI scintimammography in all cases the findings were retrospectively reviewed. Each modality was graded by two physicians specializing in nuclear medicine and two radiologists, all unaware of the pathologic results. A four-grade system(1=definitely benign, 2=probably benign, 3=probably malignant, 4=definitely malignant) was applied to those ofbreast ultrasonography and 99m Tc-MIBI scintimammography and BIRADS was applied to those ofmammography. All breast masses were confirmed by surgery (n=67) or FNA (n=14). Findings of grade 3 or 4 the four-grade system, BIRADS category 4 or 5, or positive coincidence in double and triple combination studies were defined as positive results, and on the basis of the data thus obtained, the sensitivity, specificity, positive and negative predictive value and diagnostic accuracy were calculated for each modality and for multimodality studies. RESULTS: The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of 99mTc-MIBI scintimammography were 83.6%, 88.5%, 93.9%, 71.9% and 85.2%, respectively. For ultrasonography, the corresponding figure were 94.5%, 65.3%, 85.2%, 85.0%, and 85.2%, and these for mammography, they were 87.3%, 69.2%, 87.3%, 81.8% and 80.2%. For the ultrasonography and mammography combination, the figures were 83.6%, 50.0%, 93.9%, 100.0% and 95.2%, respectively, and for 99mTc-MIBI scinti-mammography and mammography, the corresponding findings were 72.7%, 69.2%, 95.2%, 100.0% and 96.7%. For the 99mTc-MIBI scintimammography and ultrasonography combination, respective findings of were 80.0%, 61.5%, 95.7%, 94.1% and 95.2%, respectively, and in the triple modality study, respective findings of 70.9%, 50.0%, 97.5%, 100.0% and 98.1% were recorded. CONCLUSION: Among multimodality studies, sensitivity was greatest in the ultrasonography and mammography combination, which is thus extremely suitable for the diagnosis of breast cancer. The findings of two series suggest that in equivocal cases, 99mTc-MIBI scintimammography with its higher specificity and positive predictive value, is a useful adjunctive tool.