A 48-year-old Japanese woman underwent [F-18] fluorodeoxyglucose positron emission tomography (FDG-PET) as part of her medical examination. A small hot spot was detected in her right breast. Quadrantectomy with sentinel lymph node (SN) biopsy using an endoscope was performed, and ductal carcinoma in-situ of the breast was diagnosed. The tumor size was 0.9 cm in its greatest diameter, and there were no cancer cells detected in the SN on frozen hematoxylin-eosin staining and cytokeratin immunohistochemical staining. We reported this rare case of ductal carcinoma in-situ detected by FDG-PET as past of a medical checkup.