PURPOSE: The purpose of this study was to assess the incidence of invasive lobular carcinoma (ILC) and to compare the clinicopathological features and treatment results after breast conserving surgery (BCS) followed by radiotherapy between ILC and invasive ductal carcinoma (IDC). METHODS: A total of 1,071 patients who underwent BCS followed by radiotherapy were included in the study. Medical records and pathological reports were retrospectively reviewed. RESULTS: The incidence of ILC was 5.2% (n=56). Bilateral breast cancer, lower nuclear grade, and hormone receptor-positive breast cancer were more frequent in patients with ILC than in those with IDC. There were no cases of lymphovascular invasion or the basal-like subtype in patients with ILC. There were no statistically significant differences in patterns of failure or treatment outcomes between patients with ILC and those with IDC. The development of metachronous contralateral breast cancer was more frequent in patients with IDC (n=27). Only one patient with ILC developed contralateral breast cancer, with a case of ductal carcinoma in situ. CONCLUSION: The incidence of ILC was slightly higher in our study than in previous Korean studies, but was lower than the incidences reported in Western studies. The differences we observed in clinico pathological features between ILC and IDC were similar to those described elsewhere in the literature. Although there were no statistically significant differences, there was a trend toward better disease-specific survival and disease-free survival rates in patients with ILC than in those with IDC.