BACKGROUND: The timing and accuracy of axillary sentinel lymph node biopsy (SLNB) in patients who are receiving neoadjuvant chemotherapy (NACT) for breast cancer are controversial. To examine the accuracy of SLNB after NACT, the authors performed SLNB after chemotherapy on all of patients who received NACT at their institution starting in January 1997. METHODS: Seventy-nine women who underwent NACT between 1997 and 2008 comprised this study and were divided as follows: 4 women had stage I disease, 60 women had stage II disease, and 15 women had stage III disease, including 10 women who had multicentric disease. Thirty-nine women (49.4%) had clinical evidence of axillary metastasis (N1-N2) at the time of diagnosis. The regimen, the duration of treatment, and the number of cycles of NACT depended on clinical response. The choice of breast conservation therapy or mastectomy was based on the patient's response to treatment and patient preference. All patients underwent SLNB after NACT. RESULTS: Seventy-three patients underwent breast conservation therapy, and 6 patients underwent mastectomy. Sentinel lymph nodes were identified in 98.7% of patients (in 1 patient, SLNB failed to capture 1 proven axillary metastasis), and 29 patients underwent full axillary lymph node dissection. Fourteen patients (17.7%) had no residual carcinoma (invasive or ductal carcinoma in situ) in their breast, 5 patients (6.3%) had residual ductal carcinoma in situ (only), and 60 patients (75.9%) had residual invasive carcinoma. One false-negative SLNB was reported in the group of 23 patients who underwent full axillary dissection after a negative SLNB. No patient had a subsequent axillary recurrence. CONCLUSIONS: SLNB after NACT was feasible in virtually all patients and accurately selected patients who required complete level I and II axillary dissection. NACT frequently downstaged the axilla, converting patients with N1-N2 lymph node status to N0 status and also avoiding full axillary dissection in these patients.