The relationship between ABO blood groups (BG) and risk of incidence in cancers including gynecological cancers has been widely studied, showing increased incidence risk for BG A patients. As available data are inconsistent we investigated whether BG and their anti-glycan antibodies (anti-A and anti-B) have prognostic values in gynecological cancers. We retrospectively evaluated 974 patients with gynecological cancers in three cancer centers (Switzerland and Australia) between 1974 and 2014 regarding the relationships between clinico-pathological findings and the BG. Time to disease recurrence was significantly influenced by BG in patients with ovarian (n = 282) and vulvar (n = 67) cancer. BG O or B patients showed a significantly increased risk for ovarian cancer relapse compared to A, 59% and 82%, respectively (p = 0.045; HR O vs A = 1.59 (CI 1.01-2.51) and (p = 0.036; HR A vs B = 0.55 (CI 0.32-0.96). Median time to relapse for advanced stage (n = 126) ovarian cancer patients was 18.2 months for BG O and 32.2 for A (p = 0.031; HR O vs A = 2.07 (CI 1.07-4.02)). BG also significantly influenced relapse-free survival in patients with vulvar cancer (p = 0.002), with BG O tending to have increased relapse risk compared to A (p = 0.089). Blood groups hence associate with recurrence in ovarian and vulvar cancer: women with BG O seem to have a lower ovarian cancer incidence, however are more likely to relapse earlier. The significance of the BG status as a prognostic value is evident and may be helpful to oncologists in prognosticating disease outcome and selecting the appropriate therapy.