Background: The clinical significance of false-negative axillary sentinel lymph node (SLN) biopsy has yet to be established. The aim of this study was to assess the axillary recurrence rate and false-negative rate, to identify prognostic factors and to monitor survival. Methods: A prospective registry of sentinel lymph node biopsy (SLNB) procedures performed between 1998 and 2004 was analysed. All nodes retrieved were examined by haematoxylin and eosin and immunohistochemical staining. Further surgical treatment was performed only for positive SLNs. Adjuvant treatment was given according to Dutch guidelines. Results: Of 592 patients, 392 had a negative SLNB. After a median follow-up of 65 months, 11 patients developed axillary recurrence (2.8 per cent). Ten of these patients were primarily treated by simple mastectomy and therefore had no external-beam radiation therapy; no further prognostic factors could be identified. The false-negative rate was 6.9 per cent. The median time from SLNB to detection of the axillary recurrence was 27 months. The median follow-up after recurrence was 35 months, and one patient developed systemic disease. Pathology revision revealed two previously undetected micrometastases. Conclusion: Axillary recurrence and false-negative rates after SLNB increase with longer follow-up. Copyright