HYPOTHESIS It has recently been proposed that only 3 sentinel lymph nodes (SLNs) are required for an adequate SLN biopsy. Others have advocated removing all nodes that are blue, hot, at the end of a blue lymphatic channel, or palpably suspicious or that have radioactive counts of 10% or greater of the most radioactive SLN. Our objective was to determine the false-negative rate (FNR) associated with limiting SLN biopsy to 3 nodes. DESIGN Multicenter prospective study. SETTING Both academic and private practice. PATIENTS A total of 4131 patients underwent SLN biopsy followed by completion axillary node dissection. MAIN OUTCOME MEASURE The FNR associated with 3-node SLN biopsy. RESULTS Of the 4131 patients in this study, an SLN was identified in 3882 (94.0%). The median number of SLNs identified was 2; more than 3 SLNs were removed in 738 patients (17.9%). Of the patients in whom a SLN was identified, 1358 (35.0%) were node positive. The overall FNR in this study was 7.7%. In 89.7% of node-positive patients, a positive SLN was found in the first 3 SLNs removed. If SLN biopsy had been limited to the first 3 nodes, the FNR would be 10.3% (P = .005 compared with removing >3 SLNs). The FNR increased with the strategy of limiting SLN biopsy to fewer SLNs (P<.001). CONCLUSION Removing only 3 SLNs cannot be recommended, because it is associated with a substantially increased FNR.