PURPOSE: We analyzed the association of lymph node ratio (LNR) wth locoregional control (LRC) in breast cancer patients with ≥10 involved axillary lymph nodes who underwent multimodality treatment. METHODS: We retrospectively analyzed 234 breast cancer patients with ≥10 involved axillary lymph nodes between 2000 and 2011. All patients received adjuvant chemotherapy and radiotherapy (RT) after radical surgery. The cutoff value of LNR was obtained using receiver operating characteristic curve analysis. The majority of patients (87.2%) received chemotherapeutic regimen including taxane. RT consisted of tangential fields to the chest wall or intact breast, delivered at a median dose of 50 Gy, and a single anterior port to the supraclavicular lymph node area, delivered at a median dose of 50 Gy. For patients who underwent breast-conserving surgery, an electron boost with a total dose of 9 to 15 Gy was delivered to the tumor bed. RESULTS: Within a median follow-up period of 73.5 months (range, 11-183 months), locoregional recurrence (LRR) occurred in 30 patients (12.8%) and the 5-year LRC rate was 88.8%. After multivariate analysis, LNR ≥0.7 was the only independent factor significantly associated with LRC (hazard ratio, 2.06; 95% confidence interval, 0.99-4.29; p=0.05). CONCLUSION: An aggressive multimodal treatment approach showed favorable locoregional outcome in patients with ≥10 involved axillary lymph nodes. However, patients with a high LNR ≥0.7 still had an increased risk for LRR, even in the setting of current local treatments.