Despite low specificity routine mammography is the method of choice to screen women for breast cancer. In addition high frequency ultrasonography (US) or magnetic resonance imaging (MRI) can improve breast cancer diagnosis. However there is a lack of conventional imaging to improve the high rate of false positive results that make biopsy or surgery necessary. OBJECTIVE The purpose of our study was to evaluate prospectively the sensitivity, specificity, PPV and NPV of scintimammography with a new cationic complex Tc-99m-tetrofosmin. METHODS Fourtyeight patients in whom mammography and/or high resolution ultrasonography (10 MHz) revealed suspicious breast lesions were studied with Tc-99m-tetrofosmin scintimammography. In thirtyfour of them biopsy and/or surgery was performed for histological evaluation. After intravenous injection of 555 MBq Tc-99m-tetrofosmin dynamic images over three minutes (1 frame/10 sec.) planar images in anterior and lateral projections (5 min. p.i.) and SPECT imaging including 3-D-reconstruction (20 min. p.i.) were performed. Scintimammography was evaluated as negative, equivocal (+), probably (+2) or definitely (+3) positive RESULTS Scintimammography with Tc-99m-tetrofosmin was negative in 18 patients (17 t.p., 1 f.n.) and positive in 16 patients (10 t.p., 6 f.p.). The false negative scintimammography was observed in a patient with infiltrating ductal carcinoma pT1, the false positive results in a patient with fibrocystic disease; all of the five fibroadenomas were also "false" positive. Sensitivity of Tc-99m-tetrofosmin scintimammography in this prospective study was 91%, specificity 74%, PPV 63% and NPV 94%. Scintimammographic results in patients with suspicious breast lesion show, that Tc-99m-tetrofosmin accumulates in breast cancer as well as in fibroadenoma. However the high NPV of 94% excludes breast cancer in suspicious mammographic lesions in a very high degree and therefore reduces the need of biopsy and/or surgery in most of these patients CONCLUSIONS Our first results show that scintimammography with Tc-99m-tetrofosmin might play a role as further diagnostic step before surgery for women in whom mammography and/or ultrasonography show suspicious lesions.