Background: Pre-operative ultrasound-guided needle sampling (UNS) of abnormal axillary lymph nodes in breast cancer can identify patients with axillary metastases and therefore rationalize patient care and inform decision-making. To obtain tissue diagnosis, UNS can be performed by either fine needle aspiration (FNA) or core needle biopsy (CNB). However, few studies have compared the sensitivity of these techniques and the majority show no difference. Methods: All node-positive patients (those with micro- and macrometastases but not isolated tumor cells) treated at a tertiary referral center between January 2012 and December 2015 were retrospectively identified from pathology records. The result of the first axillary UNS performed on each patient was compared with postoperative histopathology results. The UNS method used was according to individual radiologist preference. Results: A total of 215 patients underwent FNA (1 patient had bilateral breast cancer and underwent bilateral FNA), and 92 underwent CNB. Sensitivity of CNB was significantly higher than FNA (83.7 vs. 69.0%, P = 0.008). The false-negative rate in the FNA group was therefore higher than in the CNB group by a factor of 2.5. There was no difference in inadequacy rate between the two techniques. There were no complications in the FNA group, and only one hematoma (which did not require operative intervention) in the CNB group. Conclusions: CNB is safe and should be the preferred technique for UNS to improve sensitivity.