PURPOSE: Neoadjuvant chemotherapy (NAC) generally induces significant changes in the pathologic extent of disease. This potential down-staging challenges the standard indications of adjuvant radiation therapy. We assessed the utility of lymph node irradiation (LNI) in breast cancer (BC) patients with pathologic N0 status (pN0) after NAC and breast-conserving surgery (BCS). METHODS AND MATERIALS: Among 1,054 BC patients treated with NAC in our institution between 1990 and 2004, 248 patients with clinical N0 or N1 to N2 lymph node status at diagnosis had pN0 status after NAC and BCS. Cox regression analysis was used to identify factors influencing locoregional recurrence-free survival (LRR-FS), disease-free survival (DFS), and overall survival (OS). RESULTS: All 248 patients underwent breast irradiation, and 158 patients (63.7%) also received LNI. With a median follow-up of 88 months, the 5-year LRR-FS and OS rates were respectively 89.4% and 88.7% with LNI and 86.2% and 92% without LNI (no significant difference). Survival was poorer among patients who did not have a pathologic complete primary tumor response (hazard ratio, 3.05; 95% confidence interval, 1.17-7.99) and in patients with N1 to N2 clinical status at diagnosis (hazard ratio = 2.24; 95% confidence interval, 1.15-4.36). LNI did not significantly affect survival. CONCLUSIONS: Relative to combined breast and local lymph node irradiation, isolated breast irradiation does not appear to be associated with a higher risk of locoregional relapse or death among cN0 to cN2 breast cancer patients with pN0 status after NAC. These results need to be confirmed in a prospective study.