A case of ductal carcinoma in situ (DCIS) with microinvasion arising in a radial scar of the breast is presented. A 57-year-old woman visited our hospital with bloody discharge from her left nipple. There were no abnormal findings on cytology, carcinoembryonic antigen (CEA) level of nipple discharge was <500 ng/ml, and mammograms were normal. After 2 years of careful periodic follow-up, spiculation without a central core appeared on mammograms. The CEA level of the nipple discharge increased to 1,000 ng/ml. Ductgraphy showed a connection between the duct with the discharge and the center of the spiculation. Since these findings suggested malignancy, she underwent segmentectomy of the breast, and pathological examination showed a radial scar and DCIS with microinvasion in the ducts within the radiating bands of fibrous tissues. We discuss the characteristics of a radial scar and its relationship to breast cancer based on our experience and a review of the literature.