Prediagnostic use of menopausal hormone therapy (MHT) has been suggested to be associated with improved survival of epithelial ovarian cancer (EOC). We investigated the potential long-term survival benefit of prediagnostic MHT use in women ≥50 years with nonlocalized EOC using the Extreme study including all women in Denmark registered with nonlocalized EOC during 2000 to 2014 (N = 3776). We obtained individual-level information on prediagnostic use of systemic estrogen therapy (ET) and estrogen plus progestin therapy (EPT) from the National Prescription Registry and estimated absolute and relative 5- and 10-year survival probabilities with 95% confidence intervals (CIs) using pseudo-values, taking into account histology, comorbidity, income and residual disease. Among women not having used prediagnostic MHT, 5- and 10-year absolute survival probabilities were 19% and 11%, respectively. Compared to MHT nonusers, prediagnostic systemic ET use for 3 to 4 years and ≥ 5 years was associated with 1.43 (95% CI: 1.01-2.02) and 1.22 (95% CI: 0.96-1.55) times higher 5-year survival probabilities, respectively. Ten-year survival probabilities were also increased but not statistically significantly. Among prediagnostic EPT users, increased 5-year (1.14, 95% CI: 0.85-1.53) and 10-year (1.38, 95% CI: 0.91-2.08) survival probabilities were observed after use for 3 to 4 years compared to MHT nonuse, whereas EPT use for ≥5 years was not associated with long-term survival of nonlocalized EOC. Our findings may suggest a better long-term survival of nonlocalized EOC in women having used long-term prediagnostic ET. However, the statistical precision of our results did not allow firm conclusions and more studies are needed.