Objective: Inflammation is associated with worse outcomes in cancer. Operations induce an acute inflammatory response and could impact the clinical outcomes in breast cancer. The neutrophil-lymphocyte ratio (NLR) is a well-known indicator of inflammation. We investigated the prognostic significance of perioperative inflammation with the NLR in breast cancer. Methods: We reviewed the clinical and pathological records of women diagnosed with invasive breast carcinoma at the Samsung Medical Center between 2000 and 2010. The NLR levels in the immediate preoperative period and the postoperative periods (1 week and 1 month) were assessed. Results: The NLRs of a total of 3,116 breast cancer patients were examined. In the univariate analysis, the NLR in postoperative week 1, total mastectomy, the presence of lymphovascular invasion, a higher nuclear grade and pathologic TNM stage, and negative hormone receptor and subtypes were factors associated with poor disease-specific survival. The NLR in postoperative week 1 remained a significant prognostic factor in the multivariate analysis. A cutoff level of 5.2, determined by the minimum p value approach, was found to be a significant level for discriminating the impact on breast cancer-specific mortality (p = 0.0116 adjusted by the Bonferroni correction). Conclusions: Immediate postoperative inflammation is an important prognostic marker in breast cancer patients.