Background : The aim of this study is to determine prognostic factors of breast cancer in Korean patients who underwent curative mastectomy. Methods : Medical records of 181 patients who underwent curative mastectomy were reviewed. Relapse-free survival and overall survival were documented for each patient. Factors influencing survival were analyzed using Cox proportional hazard model. Results : Overall 5-year survival rate was 82.0%, and 8-year survival rate was 74.7%. Multivariate analysis indicated that multiple axillary lymph node involvement (≥4), postmenopausal status, and negative estrogen receptor were independent adverse prognostic factors. The adjusted relative risks of multiple axillary lymph node involvement (≥4), postmenopausal status, and negative estrogen receptor were estimated 2.60 (95% Confidence Interval (CI): 1.28-5.30), 2.64 (95% CI: 1.46-4.79), and 2.27 (95% CI: 1.19-4.35), respectively. Conclusion : Multiple axillary lymph node involvement (≥4), postmenopausal status, and negative estrogen receptor were independent adverse prognostic factors in Korean breast cancer patients after curative mastectomy.(Korean J Med 58:446-452, 2000)