BACKGROUND: The natural history of the patients of ductal carcinoma in situ(DCIS) with microinvasion is poorly defined, and the clinical management of these patients, with particular reference to management of the axilla, has been controversial. Previous studies of this lesion have used and/or arbitrary criteria for the evaluation of microinvasion. METHODS: To compare the clinicopathologic features and the outcomes of treatment between DCIS and DCIS with microinvasion, the medical records of 101 patients of DCIS with/without microinvasion who had been treated at Yongdong Severance hospital from Apr. 1991, to Oct 1998, were reviewed retrospectively. RESULTS: The mean age of the patients of DCIS with microinvasion group was 44.8 years and that of the patients of DCIS group was 47.4 years. The peak age group of both was 5th decade. The primary tumors of DCIS-MI group were larger(2.16 vs 1.93cm) and more easily palpated(66.3% vs 36.6%) on the physical examination than that of DCIS group. The rate of the axillary lymph node metastasis was higher in DCIS-MI group.(10% vs 1.3%) In terms of nuclear grade, comedo type, hormone receptor status, and c-erbB2 immunohistochemical positivity, there were no statistical significances between DCIS group and DCIS-MI group. The recurrence rate of DCIS-MI group was higher than that of DCIS group.(10% vs 1.4%) The 5-year disease free survival rate of the DCIS group and DCIS-MI group were 98% and 89% respectively. CONCLUSIONS: Ductal carcinoma in situ with microinvasion is thought to be transitional disease entity between ductal carcinoma in situ and invasive ductal carcinoma. But the treatment options of ductal carcinoma in situ with microinvasion were similar to that of the invasive carcinoma. More long-term follow-up and multicenter studies seem to be necessary to identify differences in clinical features and to determine the optimal methods of treatment.