A 34-year-old woman with a past history of a carcinoid tumor in the right ovary presented with a right breast mass found on contrast-enhanced computed tomography (CT) of the chest. She was asymptomatic, and her blood tests were normal. The mass measured about 2 cm. Mammography showed a lobular, circumscribed, high-density mass without microcalcifications in the upper outer quadrant of the right breast. Ultrasonography showed an irregular mass with both hypoechoic and hyperechoic components with increased vascularity. The mass was well enhanced on contrast-enhanced CT and dynamic magnetic resonance imaging. At the same time, a well-enhanced small nodule was detected in the pouch of Douglas. Both of the tumors were resected, and a primary breast neuroendocrine tumor (solid neuroendocrine carcinoma) and peritoneal dissemination of the ovarian carcinoid tumor were diagnosed.