The purpose of this study was to examine the use of ultrasound (US)-guided core biopsy of axillary nodes in patients with operable breast cancer. The ipsilateral axillae of 187 patients with suspected primary operable breast cancer were scanned. Nodes were classified based on their shape and cortical morphology. Abnormal nodes underwent US-guided core biopsy/fine needle aspiration (FNA), and the results correlated with subsequent axillary surgery. The nodes were identified on US in 103 of 166 axillae of patients with confirmed invasive carcinoma. In total, 54 (52%) met the criteria for biopsy: 48 core biopsies (26 malignant, 20 benign node, two normal) and six FNA were performed. On subsequent definitive histological examination, 64 of 166 (39%) had axillary metastases. Of the 64 patients with involved nodes at surgery, preoperative US identified nodes in 46 patients (72%), of which 35 (55%) met the criteria for biopsy and 27 (42%) of these were diagnosed preoperatively by US-guided biopsy. In conclusion, US can identify abnormal nodes in patients presenting with primary operable breast cancer. In all, 65% of these nodes are malignant and this can often be confirmed with US-guided core biopsy.