Purpose: To analyse the reliability of sentinel-node biopsy (SNB) in a multicenter setting and to analyse factors potentially influencing the success rates. Material and Methods: SNB with consecutive axillary clearance was performed in 814 breast cancer patients. The detection rate and the sensitivity as well as the impact of the lymphography technique, patient selection, technical procedure and learning curves were analysed. Results: 21 centers and 80 surgeons were involved in the trial. The detection rate for the sentinel node was 84.0% for the entire group and showed a significant dependence on the lymphography technique (blue dye, 71.6%; radiolabelled tracer, 78.8%; combined technique, 89.6%) as well as the number of interventions performed. The sensitivity was 91.8% for the entire collective. Little variation for the false negative rate was observed when comparing the lymphography techniques, technical procedures, different centers or learning curves. Compared to conventional staging procedures (palpation, ultrasound), SNB showed only minor variation in the success rate even in a multicenter setting. Conclusion: SNB is a promising staging procedure for axillary involvement in breast cancer patients. Although the detection rate depends strongly on the technical procedure, the false-negative rate remains largely unaffected by potential influencing factors. Therefore, this procedure provides reliable results and appears suitable for general application. Although the impact of influencing factors on the success rates require further examination and although the oncologic role of lymphatic mapping can only be studied in prospective randomized trials, the data of this study may provide the ethical basis to initiate an observational trial following the randomization phase.