Ovarian cancer is the deadliest gynecological malignancy in Western countries. Early detection, however, is hampered by the fact that the origin of ovarian cancer remains unclear. Knowing that in a high percentage of endometrioid ovarian cancers Wnt/beta-catenin signaling is activated, and in view of the hypothesis that ovarian cancer may originate from the distal oviduct, we studied mice in which Wnt/beta-catenin signaling was activated in Mullerian duct-derived tissues. Conditional adenomatous polyposis coli (Apc) knockout mice were used to study the activation of Wnt/beta-catenin signaling in Mullerian duct-derived organs. These Pgr(Cre/+); Apc(ex15lox/lox) mice (n = 44) were sacrificed at 10, 20, 40 and 80 weeks and uterus, oviduct, ovaries and surrounding fat tissues were assessed using immunohistochemistry. Using nuclear beta-catenin staining, Wnt/beta-catenin signaling activation was confirmed in the entire epithelium of the adult Mullerian duct (fimbriae, oviduct and endometrium), but was absent in ovarian surface epithelium cells (OSEs). Besides endometrial hyperplasia, in 87.2% of mice intraepithelial lesions of the distal oviduct were found, whereas OSEs remained unaffected. In addition, 62.5% of mice developed tumors in the distal and fimbrial part of the oviduct. In the ovaries, mainly at young age, in 16.3% of mice, simple epithelial cysts were noted, which developed further into endometrioid ovarian tumors, resembling human endometrioid ovarian cancer (27.9% of mice). Next to this, locoregional growth in the utero-ovarian ligament was also shown. Here, for the first time, mutations (activation of Wnt/beta-catenin) in the distal oviduct result in precursor lesions that develop into ovarian tumors, resembling human endometrioid ovarian cancer.