PURPOSE: To evaluate the sonographic findings and detection rate of ductal carcinoma in situ (DCIS) and to compare the results with mammographic findings. MATERIALS AND METHODS: Of 134 patients with pathologically proven DCIS, 47 patients (48 breasts) who underwent sonography before surgery were included. Twenty-seven patients were asymptomatic, while 20 experienced symptoms. Whether a lesion was present, and the nature of the related sonographic finding were analyzed retrospectively. When a mass was identified by means of sonography, it was evaluated in terms of its shape, margin, echogenicity, associated microcalcifications, and intervening echogenic lines. RESULTS: Sonography detected 39/48 cases of DCIS (81%). In 24 cases, detection was based only on the presence of the mass, while in nine cases this depended on additional findings alone [periductal thickening (n=6); micronodules (n=3)]. In three cases the presence of microcalcifications alone was sufficient for detection and in the other three cases, detection was based on the presence of microcalcifications as well as on additional findings [periductal thickening (n=2); micronodules (n=1)]. Thirteen lesions (54 %) were irregular in shape, while 11 (46 %) were oval or lobulated. The margins of 17 lesions (71 %) were ill-defined, and in 18(75 %), echogenicity was slightly hypoechoic. CONCLUSION: Sonography showed that for masses identified as DCIS, the most common findings were an ill-defined margin, irregular shape, and mild hypoechogenicity. Microcalcifications were identified in 13 of 48 breasts (27%), while in some cases intervening echogenic lines and microcalcifications were the only finding. For early detection of DCIS, mammography together with sonography may be helpful.