We evaluated the relationship between the outcome of newly diagnosed ovarian cancer patients treated in 1123 German gynecology departments in 2001, and their participation in clinical trials through two German cooperative study groups. In addition, we evaluated other potential factors predicting outcome including hospital volume. The analysis was based on 476 patients from 165 hospitals and 3-year follow-up. Patients treated in study hospitals had a higher chance of receiving treatment according to national guidelines. This included a higher chance of receiving optimal staging in early stage disease and of receiving the recommended combination of surgical debulking and combination chemotherapy in advanced disease. On multivariable Cox model analysis, overall survival was significantly worse in patients treated in non-study hospitals.