Mammographic lesions can be classified into categories of high (HR), intermediate (IR) and low risk of breast cancer. We have performed 99mTc MIBI scintimammography on 85 patients with high or intermediate risk lesions in order to verify its ability to diagnose cancer before biopsy. The scintimammography was performed in prone lateral view; all the patients were submitted to excisional biopsy. HR lesions showed 86% of cancers and scintigraphic accuracy of 0.81. The accuracy of scintimammography was 0.97 in lesions larger than 1 cm. IR lesions showed 47% of cancer with scintigraphic accuracy of 0.95. The scintigraphic sensitivity was 0.97 lesions larger than and 0.50 in lesion smaller than 1 cm, whereas the specificity was always about 90%. Our results suggest that scintimammography can substantially decrease the need of biopsy for breast cancer diagnosis.