Purpose: Piccolo et al. advocated the usefulness of Tc-99m-MDP breast scan in differential diagnosis of breast mass with high accuracy. But there are little or no follow-up studies about it as we know. We studied Tc-99m-MDP uptake pattern and lesions/background ratio in patients complaining palpable breast lesions to evaluate the clinical usefulness of Tc-99m-MDP scan. Materials and Methods: Total 34 patients were studied with physical examination, mammogram and Tc-99m-MDP scan prospectively. Anteroposterior and both lateral view of breast were obtai- ned 5 minutes after iv injection of 740 MBq Tc-99m-MDP. Breast uptake pattern of Tc-99m- MDP was analyzed by a grade system: 0=no uptake, grade 1=bilateral diffuse uptake, grade 2=asymmetric faint uptake, grade 3=focal hot uptake. 20 cases were pathologically confirmed by excision biopsy or aspiration biopsy. 14 cases were normal in physical examination and mammo- grain. Results: Pathologic results showed 7 carcinomas, 6 benign solid tumors, and 7 fibrocystic changes. Grade 3 pattern of Tc-99m-MDP uptake was noted in 4/7 carcinomas, 3/6 benign solid tumors, and 1/7 fibrocystic changes. Grade 2 pattern was 2/7, 0/7, 3/7 respectively. The average L/B ratio was 1.66 in carcinomas, 1.68 in benign solid masses, 1.20 in fibrocystic diseases, 1.05 in normal patients. L/B ratio was higher in carcinoma and benign mass groups than in fibrocystic change and normal control groups(p=0.005). But there was no statistical difference between L/B ratio of malignant mass group and benign mass group. Conclusion: Tc-99m-MDP scan is not suitable to routine clinical use for breast mass diagnosis. It might be used in limited conditions when whole body bone scan is planned.