Mucocele-like tumor (MLT) of the breast is a rare neoplasm. Although this lesion was considered benign when first described, the concept of a pathologic continuum with mucinous carcinoma was evident in subsequent reports. Only a few cases of MLT have been reported in Korea. We describe a case of MLT associated with ductal carcinoma in situ and mucinous carcinoma in a 34-yr-old female. Histological examination showed multiple mucus-filled cysts of varying size. Extravasated mucin was present in the surrounding stroma. The lining of the cysts in most areas were of flat or cuboidal epithelium and devoid of cellular atypia. The lining epithelium showed proliferative change ranging from atypical ductal hyperplasia to ductal carcinoma in situ, micropapillary type. A microscopic focus of mucinous carcinoma within MLT was also noted. None of the lesions exhibited epithelial reactivity for p53 protein. The patient is alive and well without evidence of disease 54 months after initial treatment. This case supports the concept that MLT encompasses a spectrum of pathologic lesions including benign tumor, atypical ductal hyperplasia, ductal carcinoma in situ, and mucinous carcinoma.