Objective: The purpose of this study is to examine the oncological safety of breast conserving surgery (BCS) for patients with multifocal breast cancer. Summary Background Data: Few studies have reported about BCS for multifocal breast cancer. BCS for multifocal cancer has a risk of local failure in previous reports, whereas recent studies reported the feasibility of BCS. However, because all studies have dealt with a small number of patients, multifocal breast cancer is still considered a relative contraindication for BCS. Methods: This retrospective study includes 478 patients with multifocal breast cancer who underwent BCS or mastectomy and 930 with unifocal cancer who underwent BCS for stage 0-II. Multifocal cancer was defined as 2 or more distinct cancers in the same quadrant. Of 478 patients, 147 underwent BCS and 331 underwent mastectomy. We compared the local recurrence rate (LRR), disease free survival, and overall survival for BCS with mastectomy for multifocal cancer. In addition, the LRR of BCS for multifocal cancer was compared for unifocal cancer. Results: There is no significant difference in stage distribution and other clinical and pathologic characteristics except Her-2/neu for stage IIA between BCS and mastectomy for multifocal caner. The mean follow-up period was 59.33 months (range, 1.00-177.20) for breast conserving group and 64.98 months (range, 6.23-196.03) for mastectomy group. The 5-year overall survival was 93.38% for BCS and 94.53% for mastectomy (log rank P = 0.208). The 5-year disease-free survival was 89.08% for BCS and 91.88% for mastectomy (log rank P = 0.451). The local failure occurred in 3 (2.0%) of 147 patient underwent BCS, 3 (0.9%) of 331 patients underwent mastectomy (P = 0.378). Compared with BCS for unifocal cancer patients, the LRR of patients with multifocal cancer was not statistically different (2.0% for multifocal, 1.3% for unifocal; P = 0.445). Conclusions: Our study demonstrates that BCS for multifocal breast cancer is oncologically safe in selected patients.