PURPOSE: Medullary carcinoma of breast was known to have a better prognosis than other breast cancer, but the histopathological definition of medullary carcinoma has varied with time. This study was performed to clarify the clinicopathologic features of medullary breast cancer. MATERIALS AND METHODS: Twenty cases of breast cancer originally were diagnosed as medullary carcinoma at the Department of Surgery, Seoul National University Hospital from Jan. 1985 to Jun. 1995. The whole cases were reviewed and reclassified using the strictly defined histologic criteria applied by Ridolfi et al. RESULTS: When reclassified, 16 tumors fulfilled the criteria of typical medullary cancer. But the rest 4 tumors were found to be nonmedullary cancer. The patients ranged from 29 to 69 years in age with an average of 49. The main symptom was the painless mass. The diameter of the tumor ranged from 1 to 8 cm with a mean size of 2.7 cm. The axillary lymph node was positive in three cases. The estrogen receptor was positive in 10%, and the progesterone receptor was positive in 20% of the cases. There were no local recurrences or distant metastasis during a mean follow-up period of 5.5 years.. All patients survived until the last follow-up. CONCLUSION: Medullary breast cancer has good prognosis but strict, uniform histopathological diagnostic criteria are needed.