The aims of study were to compare the rates of ipsilateral breast tumor recurrence (IBTR), for patients treated with either quadrantectomy or lumpectomy at a single institution, and to identify predictors of IBTR after breast-conserving therapy (BCT). The database and medical records of 807 patients who underwent BCT for breast cancer between 1987 and 2002 were reviewed. The age of the patient, tumor size, lymph node status, extensive intraductal component (EIC), re-excision, final margin status, and the extent of surgery were examined in reference to IBTR rates. Of the total 807 patients, 456 (56.5%) had undergone quadrantectomy and 351 patients (43.5%) had lumpectomy. Apart from the higher re-excision rate in the lumpectomy group (p < 0.001), there were no significant differences in clinical and pathologic characteristics between the patients in the two groups. At the median follow-up time of 72 months, 28 cases of IBTR (3.4%) and 56 cases of systemic recurrence (6.9%) had developed in 72 patients (8.9%). On multivariate analysis, young age (< or =35) (p = 0.041), positive lymph node (p < 0.001), and the presence of EIC (p = 0.004) were independent predictors of IBTR. However, we could not find a significant difference in IBTR rate between the two groups (p = 0.546). Thus, the extent of breast surgery (quadrantectomy or lumpectomy) did not make a significant difference in IBTR if adequate surgical margins could be achieved.