PURPOSE After a report from the Women’s Health Initiative (WHI) in 2002, a precipitous decline in menopausal hormonal therapy (MHT) use in the United States was linked to a decline in breast cancer incidence rates. Given that MHT use is also associated with increased ovarian cancer risk, we tested whether ovarian cancer incidence rates changed after 2002. METHODS Using the North American Association of Central Cancer Registries database (1995 to 2008; N = 171,142 incident ovarian cancers), we applied standard analytic approaches and age-period-cohort (APC) models to estimate ovarian cancer incidence rate changes before (1995 to 2002) and after (2003 to 2008) the WHI report. Results Among women age ≥ 50 years, age-standardized ovarian cancer incidence declined by 0.8% per year (95% CI, -1.8% to -0.5% per year) before the WHI announcement; after the WHI report, the rate declined by 2.4% per year (95% CI, -2.5% to -2.2% per year). APC models confirmed an accelerated decline in ovarian cancer incidence after the WHI report, adjusted for age and birth cohort effects. This sudden change was notable among women most likely to have used MHT (ie, women age 50 to 69 years, white women, and residents of regions with highest MHT prescription frequency). The largest changes were found for the endometrioid histologic subtype. CONCLUSION After a marked reduction in MHT use around 2002, ovarian cancer incidence rates demonstrated an accelerated decline, with the largest changes for endometrioid carcinomas. This strong temporal association, although not proving a causal role of hormones in ovarian carcinogenesis, suggests that future analytic research supporting cancer control efforts should clarify the role of hormonal exposures on the development and behavior of subtypes of ovarian cancer.