PURPOSE: To evaluate the validity of shape, margin, internal echo, retrotumoral echo, and depth/width ratio as the ultrasound criteria for the differential diagnosis between malignant and benign breast tumor. MATERIALS AND METHODS: Pathologically proved 40 breast cancers and 55 fibroadenomas were retrospectively analyzed according to the following five major criteria for benignancy/rnalignancy: 1. shape (regular/irregular), 2. margin (sharp/indistinct), 3. internal echo (fine homogeneous/coarse heterogeneous), 4. retrotumoral echo (enhancement/attenuation), 5. depth/width (D/W) ratio (<0.7/>0.7). RESULTS: The sensitivity, specificity, positive predictive value, and negative predictive value were 78%, 87%, 82% 84% for shape;85%, 84%, 79%, 88% for margin; 33 %, 64%, 39 %, 56 % for internal echo; 43 %, 91 %, 77 %, 68 % for retrotumoral echo;and 70%, 71%, 64%, 76% for D/W ratio. CONCLUSION: Of the five major criteria, shape, margin and D/W ratio of 0.7 are proved to be good diagnostic criteria, and retrotumoral echo is less sensitive but specific criterion for the ultrasonographic diagnosis of breast cancer. Internal echo pattern is proved not to be a good criterion.