Objectives: To evaluate the efficacy of ultrasound (US) and US-guided fine-needle aspiration (US-FNA) for axillary nodal staging in breast cancer patients. Methods: A retrospective study of breast cancer patients at our institution from January 2007 to December 2009 revealed 449 cases in which axillary US was performed. The US appearance of the axillary lymph nodes was divided into 4 categories: suspicious, borderline, benign, and not visible. The results were compared with the final pathologic outcome and correlated with the tumor size on US and the pathologic nodal stage (pN). Results: Among the 449 patients, the lymph nodes were: not visualized in 124, suspicious in 180, borderline in 39, and benign in 106 cases. The overall sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of US alone and combined US/US-FNA was 69.1%, 83.3%, 86.8%, 63%, and 74.6% and 69.1%, 100%, 100%, 67.2%, and 81.1%, respectively. The sensitivity of US increased with increasing tumor size and pN. A negative or benign US (combined n = 230) was associated with the pN0, pN1, pN2, and pN3 stage in 146, 66, 13, and 5 cases, respectively. Conclusions: Axillary staging using US criteria is about 70% sensitive and its sensitivity increases with increasing tumor size and pN stage.