Background: ~25% of patients with stage III OC are reported to be alive ≥ 10 years after diagnosis in registry studies¹. Some have long term disease-free survival (LTDFS) without recurrence and others have recurrent active disease but the proportions of each is unclear. We propose to determine the proportion, characteristics, and predictors of long term survival in patients with stage III ovarian cancer (OC) enrolled in clinical trials who are ≥ 10 years LTDFS . Methods: Data from 3 NRG/GOG trials (104, 114, and 172) which enrolled patients to intraperitoneal (IP) vs. intravenous (IV) chemotherapy were analysed. Demographics and clinic-pathologic characteristics of patients living ≥ 10 years were tabulated. Using a landmark approach at 10 years, Cox regression survival analysis was performed to evaluate independent prognostic factors that predict LTDFS. Results: Of 1,229 stage III OC patients, 18.8% (232/1229) were alive ≥ 10 years. Of these, 13.7% (n = 168) had LTDFS ≥ 10 years and 5.2% (n = 64) had recurrent disease. Compared to the overall study group, the LTDFS ≥10 years patient had a median age of 54.8 vs. 57.2 years (p < 0.001), gross residual disease after primary surgery 42.3% vs. 45.8% (p = 0.027); serous cell type 62.5% vs. 68.4%; endometrioid 14.3% vs. 9.4% (p = 0.035), well differentiated cancers 12.5% vs. 8.5% (p < 0.001), respectively. Of the LTDFS patients, 45.2% were treated with IP and 54.8% with IV chemotherapy (p = 0.3). Age (HR = 1.077; 95% CI = 1.03–1.12; p < 0.001) was the only independent prognostic factor for LTDFS ≥10 years on multivariate Cox analysis. Conclusions: Approximately 14% of stage III ovarian cancer patients were in LTDFS at ≥10 years and an additional 5% were alive with recurrent disease. Younger age at diagnosis was the only independent prognostic factor for LTDFS ≥10 years. Further work is needed to understand characteristics and predictors of exceptional responders and whether they could be identified at initial diagnosis. ¹ Baldwin et al Obstetrics & Gynecology: 2012: 120; 3: 612–618