The quantitative immunofluorescence assay of serous ovarian cancer tissue for the expression of estrogen receptors (ERα and ERβ) revealed a higher expression level of ERβ in comparison with ERα in all surgical tumor samples investigated. Significant differences in the expression level of the markers were detected "from tumor to tumor." A high expression level of both ERα (≥ 25%) and ERβ (≥ 44%) in the tumor predicts a significantly longer progression-free survival time (p < 0.01) in the patients after the first line of platinum and taxane-based adjuvant chemotherapy.