Ovarian cancer is a gynecologic cancer with a high mortality rate. This shows the need of effective screening methods and reliable cancer markers for ovarian cancer staging and appropriate effective cancer treatment. Expression of estrogen receptor alpha and beta was studied by immunhistochemical analysis of 100 ovarian cancer tissue samples. In this study on 100 serous ovarian cancer tissue samples from patients with defined clinicopathologic features, a significant association of ER-alpha expression with ovarian cancer grading (p = 0.004), progression-free survival (p = 0.007), and cause-specific survival (p = 0.001) was demonstrated. Expression of ER-beta was found to be associated with the metastatic lymph node status (p = 0.006). Immunohistochemical analysis of ER might be used as an easy, simple and highly efficient marker to identify high-risk patients and may aid in the selection of patients for a more aggressive adjuvant therapy. Furthermore, patients that show a positive ER-alpha immunostaining can be selected for a specific anti-hormonal therapy, as already performed for breast cancer patients.