The purpose of this study was to determine the usefulness of ultrasound (US) as an adjunct to mammography (MMG) in the surgical treatment planning for patients with ductal carcinoma in situ (DCIS) of the breast. A total of 119 patients diagnosed with DCIS, who were treated between 1999 and 2002, were identified from the institutional database. US and MMG size of suspicious abnormalities, pathologic tumor size, and findings of axillary US and surgical axillary evaluation were analyzed. The median size difference of US versus pathologic tumor size and MMG versus pathologic tumor size was 1.0 and 2.0 cm, respectively. Correlation coefficients for US versus pathologic tumor size and MMG versus pathologic tumor size were 0.53 and −0.09, respectively. The negative and positive predictive values of axillary US to predict nodal disease were 93% and 27%, respectively. US evaluation appears to be a useful tool in conjunction with MMG in determining the extent of disease in patients diagnosed with DCIS. However, the low positive predictive value of US for evaluating metastases to axillary lymph nodes does not justify the routine use of this modality for axillary evaluation in patients with DCIS. Therefore the use of US for patients diagnosed with DCIS needs further investigation.