Patients with breast lesion suggestive of malignancy underwent Tc-99m MIBI scan in order to assess the value of this technique in the detection of breast carcinoma and axillary lymph node metastasis. One hundred five patients with breast lesion underwent 99m-MIBI scan before biopsy. 20 mCi of Tc-99m MIBI was given intravenously in contralateral arm of the breast lesion and planar prone lateral and supine anterior views for 10 minutes each were taken. Pathologic diagnoses were carcinoma in 77 breasts of 76 patients and benign in 29 patients. Pathologic types were DCIS in 4, IDC in 62, mucinous carcinoma in 3, medullary carcinoma in 2 and others in 6. The pathologic tumor status was DCIS in 4, T1 in 27, %2 in 30, T3 in 6, T4 in 4 and Tx is 6 cases. all patients with multiple lesions were positive. The sensitivity of Tc-99m-MIBIscan was 95%(73/77) and specificity was 69%(20/29). Sensitivity of mammography and ultrasonography were 85% and 82%. Axillary metastasis study showed 68% sensitivity and 92% specificity. The Tc-99m MIBI scan is a highly effective method in the diagnosis of breast cancer.