Purpose: Axillary lymph node status is one of the most important prognostic factors in early-stage breast cancer. Sentinel lymph node biopsy is used to determine the status of axillary nodes. There is a subset of patients in whom preoperative identification of nodal metastases could lead directly to axillary dissection. Preoperative axillary ultrasonography is a generally available noninvasive technique for assessing nodal status. Materials and Methods: Based on retrospective data, we analyzed the sensitivity, specificity, positive and negative predictive values, and accuracy of preoperative ultrasonography performed at our institution on patients who underwent surgery for breast cancer from January 2009 to December 2010 (24 months). A total of 620 axillary ultrasonographic examinations were included, and results were compared with pathological exam. Results: Ultrasonography revealed unremarkable findings in 500/620 (80%) axillae. There were 368 true negatives, 91 true positives, 29 false positives and 132 false negatives. Sensitivity was 40.8% and specificity 92.7%. Preoperative ultrasonography had a positive predictive value of 75.8%, and a negative predictive value of 73.6%, with an accuracy of 74.0%. Conclusion: This sample from our institution represents one of the largest reported in the literature and shows that preoperative axillary ultrasound is a method with high specificity but relatively low sensitivity for detecting the presence of axillary metastasis.