Background. Technetium-99m (99mTc) tetrofosmin scintigraphy is a new imaging method for the diagnosis of various malignancies, such as lung, thyroid, and most frequently breast neoplasms. The aim of this study was to evaluate the diagnostic reliability of 99mTc-Tetrofosmin breast scintigraphy in the detection of malignant breast disease. Methods. 99mTc -Tetrofosmin scintimammography (SMM) was performed in 28 patients with 30 breast lesions suspicious for malignancy. Standard mammography (MM) was also done. After surgery, the results of SMM and MM were compared to definitive histopathological findings as the "gold standard". After intravenous injection of radiotracer, SMM was performed in prone and supine views of the thorax, using large field-of-view Gamma camera. Results. The results of SMM were interpreted visually and semiquantitatively, and evaluated as positive or negative. Sensitivity, specificity and accuracy, positive (PPV) and negative predictive value (NPV) were obtained in relation to histopathology. After comparing the results of SMM and MM, SMM was proved more sensitive (95% for SMM vs. 80% for MM), while the specificity of both methods was similar. Conclusion. The results of this study indicate that the contribution of SMM as a nuclear medicine procedure has its place in the diagnostic protocol for patients suspected of malignant breast cancer.