BACKGROUND: The ACOSOG Z0011 trial (Z0011) expanded our thinking about breast cancer (BC) and showed that limited metastatic disease left behind in the axilla did not compromise oncological safety in a selected group of patients. The aim of the current study was to assess the potential impact of Z0011 on clinical practice by testing the applicability of its criteria to a European patient population. METHODS: We reviewed a consecutive series of 389 sentinel lymph node biopsies (SLNB) performed for invasive BC at the University Hospital Basel between 2003 and 2009 (65.6% of all surgically treated patients, n = 593). RESULTS: When compared to the axillary lymph node dissection (ALND) arm of Z0011, our patients had significantly less advanced LN involvement (≥ 3 LN: 8.5% vs. 21.0%, p = 0.048). Thirty-five patients (9.0%) met the Z0011 inclusion criteria and had 1-2 SLNs with macrometastases (5.9% of all surgically treated BC patients). If the inclusion criteria of Z0011 had been applied, a considerable number of LNs would have been missed in two cases (0.5% of all SLNBs). CONCLUSIONS: The application of the Z0011 led to the omission of completion ALND in less than 10% of all SLNB procedures (<6% of all surgically treated BC patients); therefore, we do not think that the perception of Z0011 as "practice changing" is justified. On the other side, skeptics of the routine implementation of the Z0011 protocol may overestimate its potential hazards. When performing a thorough preoperative clinical axillary staging, the number of patients who would have been undertreated is minimal.