PURPOSE: To evaluate the ultrasonographic (US) findings of ductal carcinoma in situ (DCIS) of the breast and its usefulness. MATERIALS AND METHODS: US and mammographic findings of 20 cases of pathologically proven DCIS were retrospectively evaluated. The presence of nodule, microcalcification and ductal dilatation were examined in US and compared with mammograms. RESULTS: In US, 17 (85%) of 20 cases showed single (n=14, 82%) or multiple nodules (n=3, 18%). Five of the 17 cases showed echogenic dots suggesting microcalcifications within the mass. Three cases missed on US showed microcalcification only on mammogram. Other findings were heterogeneous internal echo (n=16, 94%), irregular mass margin (n=14, 82%), and ductal dilatation (n=4, 24%). Mammogram showed abnormal findings in 15 cases (75%); nodule without microcalcification (n=7, 47%), microcalcifications only (n=5, 33%) and nodules with microcalcifications (n=3, 20%). Five cases missed on mammography showed single (n=3) or multiple nodules (n=2) without microcalcification on US. CONCLUSION: Ultrasongram does not show specific findings of DCIS, but it is superior to mammogram in the detection and characterization of DCIS manifested as only nodules without microcalcification.