The aim of this study was to evaluate the value of Ultrasonography (US) guided fine-needle aspiration (FNA) of the axilla to identify breast cancer patients with extensive nodal involvement. A prospective database of breast cancer patients who underwent US-guided FNA of suspicious nodes, diagnosed between 2000 and 2007 was analyzed. Patients with a negative axillary US or C2 (benign) FNA result underwent SLNB. Patients with C5 (malignant) FNA result underwent axillary lymph node dissection (ALND). All SLNB positive patients underwent completion ALND. The number of positive nodes after ALND was documented and analyzed. A total of 1,448 patients were included. US sensitivity was 34.2 %, specificity was 96.2 % and the accuracy was 71.7 %. For US-guided FNA this was 89, 100 and 90.4 %, respectively. In 234/1,448 patients (16.2 %) US-guided FNA was performed. A total of 19/41 C2 patients (46.3 %) had a positive SLNB. A median of 1 (range 1-6) positive node was found. A median of 4 (range 1-30) positive nodes were found in 158 C5 patients. In 376/1,214 patients with a negative US, SLNB was positive. A median of 2 (range 1-38) positive nodes were found. There was a significant difference in nodal involvement between C5 and SLNB positive patients (p = 0.043 and p < 0.0001, respectively). Ultrasound-guided FNA is a highly specific technique for detecting axillary metastases in breast cancer patients. Patients with US-guided FNA-diagnosed axillary metastases have significantly more involved nodes compared to SLNB positive patients.