PURPOSE: The most important prognostic factor in patients with operable breast cancer is lymph node involvement. The 6th edition of AJCC categorizes metastasis to more than 10 nodes as N3, or stage IIIc. Such patients have a high risk of recurrence and death. The purpose of this study was to evaluate the prognosis of these N3 patients. METHODS: Between 1991 and 2004, 141 patients with 10 or more positive lymph nodes were treated at our institution, and we retrospectively reviewed their medical records. We analyzed patient age, tumor size, number of metastatic lymph nodes, hormone receptor status, C-erb-B2 status, and treatment modality. Survival was calculated using the Kaplan-Meier method on SPSS 12.0 software. RESULTS: The median follow-up duration was 55.0 months (range 3~182 months); 78 patients had recurrence, and 44 patients died. The 5-year disease-free survival and 5-year overall survival rates were 49.4% and 64.6%, respectively. The only prognostic factor for disease-free survival was tumor size. In patients with tumors less than 2 cm in size, the 5-year disease-free survival was 68.9%, while the 5-year disease-free survival was 27.7% in patients with tumors larger than 5 cm. Hormonal receptor status, C-erb-B2 status, number of metastatic lymph nodes, and treatment modality were statistically insignificant in predicting disease-free survival. None of these factors was significant for predicting overall survival, either. CONCLUSION: The 5-year disease-free survival rate was 49.4%, and it was influenced only by tumor size. Adjuvant chemotherapy and adjuvant radiotherapy were not independent factors predicting survival. Early breast tumor detection is important in N3 breast cancer patients.