PURPOSE: We wanted to evaluate the sensitivity and specificity of screening mammography and ultrasonography for breast examinations and we assessed the clinical usefulness of breast ultrasound for cancer screening. MATERIALS AND METHODS: Of all the women who visited the health promotion center of seven medical institutions from Mar 2004 to Feb 2005, we compared the sensitivity and specificity between a single use of mammography and mammography with ultrasonography for the patients who underwent both mammography and ultrasonography. Here, the reference criteria were the follow-up and the histopathology, which were performed after one year. RESULTS: A total of 1123 patients underwent both mammography and ultrasonography and they could be followed up for a year. For the 1123 patients who underwent both mammography and ultrasonography, the sensitivity and specificity of a single use of mammography were 14.3% and 86.9%, respectively. The sensitivity and specificity of mammography with ultrasonography were 85.7% and 85.9%, respectively. These results showed that the sensitivity was significantly increased when mammography was combined with ultrasonography (< 0.05). CONCLUSION: The sensitivity was improved for the cases that underwent both mammography and ultrasonography.