The pathology database extended to 98 patients. Multiple duplications were identified and correctly identified preoperative C5 axillae were excluded. A final cohort of 43 positive SNB (false negative US) assessments were identified from the 266 SNB procedures performed in the time period. The 13 operators included locums, trainees, multi-professionals and external consultant staff. All operators had at least one false negative assessment of the axilla. Positive nodal histology was reported for 14 cases as micro-metastases or isolated tumour cells (ITC) and in 29 cases as macro-metastases/extranodal spread or multiple involved nodes. Eleven per cent of SNBs were considered false negative US assessments (29/266). Our NPV calculates at 83.8% (43 patients = 223/266) for all surgical positive axillae and 89% with exclusion of micro-metastases/ITC.