This article summarizes the relative pros and cons surrounding the timing of sentinel lymph node (SLN) biopsy in patients undergoing neoadjuvant chemotherapy. Several institutions initiated prospective trials of SLN biopsy performed after neoadjuvant chemotherapy in conjunction with a completion axillary lymph node dissection, with the goal of ultimately showing that SLN biopsy could be safely and accurately performed after the patient completed systemic therapy. Other institutions adopted a policy of performing SLN biopsy before initiation of chemotherapy. This avoided the issue surrounding the accuracy of SLN biopsy after chemotherapy and potentially provided information that might influence adjuvant therapy decisions. This article addresses the clinical questions regarding the 2 approaches including the accuracy of the procedure and the prognostic information gleaned.