PURPOSE: The effect of delays in surgical treatment on survival outcomes in patients with breast cancer remains uncertain, but it is an issue of importance to both patients and clinicians. The purpose of this study was to determine the impact of delayed surgical treatment on survival and tumor progression such as changes in tumor size and lymph node metastasis. METHODS: Among 1,219 patients who underwent breast cancer surgery at Asan Medical Center between January 2008 and December 2008, 1,074 patients were finally included in the study following the application of inclusion and exclusion criteria. Patients were divided into two groups based on the interval between diagnosis and surgery: ≤30 days (group 1) and >30 days (group 2). We retrospectively analyzed clinical characteristics, changes in tumor size and axillary lymph-node status, and overall survival (OS) and disease-free survival (DFS) rates. RESULTS: Between group 1 and group 2, there were no differences in clinical characteristics or in changes in tumor size between findings based on ultrasonography (USG) with biopsy at diagnosis and pathologic results (p=0.134). Furthermore, changes in tumor size and lymph-node status between USG results at Asan Medical Center and pathologic results also showed no differences (p=0.249 and p=0.233, respectively). There were also no significant differences in DFS (p=0.395) or OS (p=0.813). CONCLUSION: Our study showed that short-term delays of ≤2 months between diagnosis and surgery for breast cancer do not negatively affect cancer progression or survival rates.