© 2018 Purpose: We sought to determine the level of concordance among surgeons' assessment of residual disease (RD) and pre-treatment computed tomography (CT) findings among women who underwent optimal surgical cytoreduction for advanced stage ovarian cancer. Methods: This is a post-trial ad hoc analysis of a phase 3 randomized clinical trial evaluating the impact of bevacizumab in primary and maintenance therapy for patients with advanced stage ovarian cancer following surgical cytoreduction. All subjects underwent imaging of the chest/abdomen/pelvis to establish a post-surgical baseline prior to the initiation of chemotherapy. Information collected on trial was utilized to compare surgeon's operative assessment of RD, to pre-treatment imaging. Results: Of 1873 enrolled patients, surgical outcome was described as optimal (RD ≤ 1 cm) in 639 subjects. Twelve patients were excluded as they did not have a baseline, pretreatment imaging, leaving 627 participants for analysis. The average interval from surgery to baseline scan was 26 days (range: 1–109). In 251 cases (40%), the post-operative scan was discordant with surgeon assessment, demonstrating RD > 1 cm in size. RD > 1 cm was most commonly identified in the right upper quadrant (28.4%), retroperitoneal para-aortic lymph nodes (RD > 1.5 cm; 28.2%) and the left upper quadrant (10.7%). Patients with RD > 1 cm on pre-treatment CT (discordant) exhibited a significantly greater risk of disease progression (HR 1.30; 95% CI 1.08–1.56; p = 0.0059). Conclusions: Among patients reported to have undergone optimal cytoreduction, 40% were found to have lesions >1 cm on postoperative, pretreatment imaging. Although inflammatory changes and/or rapid tumor regrowth could account for the discordance, the impact on PFS and distribution of RD may suggest underestimation by the operating surgeon.