Purpose : The purpose of this study is to evaluate the accuracy of differentiation between benign andmalignant clustered microcalcifications without mass on mammogram. Material and Methodes : Fourty six mammogramsof 44 patients showing clustered microcalcifications without mass were interpreted blindly by five independentobservers majoring in breast imaging from different institutions. Twenty two were malignant (10 infiltratingductal carcinomas, 12 intraductal carcinomas) and 24 were benign (all fibrocystic disease). The observers judgebenignancy or malignancy of microcalcifications. The authors assess the accuracy of differential diagnosis ofclustered microcalcifications. Result : Of 24 cases proved benign microcalcifications, five radiologists correctlyinterpreted 20 on average as benign and of malignant 22 cases, 16 on average were correctly interpreted asmalignant. The diagnostic accuracy of malignant microcalcifications was 71.8% on average(63.6%~81.8%) and thediagnostic accuracy for benign microcalcifications was 83% on average(71%~ 92%). It was 9 among total 46 casesthat were misinterpreted by more than three radiologists. Among these 9 cases, malignant microcalcifications thathad been misinterpreted as benign were seven, benign microcalcifications misinterpreted as malignant were two.Conclusion : The diagnostic accuracy of clustered malignant microcalcifications(71.8%) without mass on mammogramwas lower than that of benign microcalcifications(83.3%). So, in case of suspected malignant microcalcification onmammogram, it is preferable that along with magnification view, histopathologic confirmation by core biopsy mustbe obtained.