The contemporary onset of primary multiple neoplasia in the same person, is an infrequent and still unclear phenomenon, in which family histories seem to have a remarkable role. We present the case of a 57-year-old woman with two simultaneous carcinomas: breast cancer and ovarian cancer. In particular we highlight the role played by echography in the diagnosis. After mastectomy for invasive ductal cancer of the left breast, an echotomography for post-operative staging led to the diagnosis of bilateral ovarian cystadenocarinoma. An ascitic flap was detected in the right subdiaphragmatic area, thus echography was extended to the whole abdomen and pelvis. The cystadenocarcinoma has a pathogenomic echo-pattern. In the case of multilocular ovarian masses of 5 cm or more, with complex (fluid-solid) echostructures and endocystic vegetation, cystadenocarcinoma is confirmed when echography reveals ascitic effusion. The ovarian cystadenocarcinoma is, in fact, frequently associated with peritoneal carcinomatosis.