This study has aimed to determine the diagnostic value of the scintimammography with 99mTc-MIBI in the detection of primary breast cancer and to verify its clinical usefulness. Sixty-three female patients (age range 27-83) with breast lesions detected by physical examination, ultrasonography, and/or mammography were prospectively included in this study. An anterior and prone lateral planar 99mTc-MIBI scintimammography was performed on all patients. The final diagnosis was achieved by histopathological examination in 49 patients and clinical followup (at least one year) in 14 patients. Histopathological diagnosis confirmed that 15 lesions were malignant and 34 lesions were benign. All the malignant lesions were larger than 1 cm. The 99mTc-MIBI scintimammography showed increased focal uptake in 17 lesions (two of them were benign and the other 15 were malignant). The diffuse heterogeneous uptake pattern was considered as benign. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy values for breast carcinoma were calculated as 100%, 96%, 88%, 100%, 97%, respectively. We concluded that 99mTc-MIBI scintimammography could be a valuable method in the differentiation of malignant breast neoplasm larger than 1 cm size from benign ones, especially when the uptake pattern was considered.