Serous ovarian cancer is suggested to develop from epithelium embryologically derived from the Müllerian ducts. The aim of the current study is to thoroughly, analyze the epithelium derived from the Müllerian ducts (cervix, endometrium and fallopian tubes) in serous ovarian cancer patients. Sixty women diagnosed with serous ovarian carcinoma were included in this multicentre, observational study. Tissues were embedded completely for histological assessment, in accordance with the SEE-Fim and SEE-End protocol (Sectioning and Extensively Examining of the Fimbriated end; and-Endometrium), and prevalence of cervical, as well as endometrial and tubal pathology was analyzed. In 31 (52%) cases, a pathologic lesion was identified, and in 16 (27%) of these cases coexistence of pathologic lesions. In 1 case, severe dysplasia was found in the cervix, in 9 (15%) cases endometrial intraepithelial carcinoma, in 19 (32%) cases atypical hyperplasia, and in 23 (43%) cases serous tubal intraepithelial carcinoma. Serous tubal intraepithelial carcinoma was seen significantly more often concurrent with endometrial atypical hyperplasia or endometrial intraepithelial carcinoma than with benign endometrium (64 vs 28%; P=0.01). To conclude, histological assessment of epithelium derived from Müllerian ducts of serous ovarian cancer patients resulted in the identification of endometrial intraepithelial carcinoma, serous tubal intraepithelial carcinoma and/or endometrial atypical hyperplasia in more than half of cases. Coexistence of these pathologic lesions was common, and might represent an effect of field carcinogenesis or tumor implantation of migrating cells.