Background: Bilateral oophorectomy (BO) confers immediate estradiol loss. We examined prevalence and predictors of Alzheimer's disease (AD) in women with early BO comparing their odds ratios of AD to those of women with spontaneous menopause (SM).Methods: A cohort from UK Biobank (n = 34,603) included women aged 60 + at baseline with and without AD who had early BO or SM. AD was determined based on AD related ICD-10 or ICD-9 code. We used logistic regression to model the association of menopause type with AD. Model predictors included age, education, age at menopause, hormone therapy (HT), APOE4, body mass index (BMI), cancer history, and smoking history.Results: Those with early BO had four times the odds of developing AD (OR = 4.12, 95% CI [2.02, 8.44]) compared to those with SM. APOE4 (OR = 4.29, 95% CI [2.43, 7.56]), and older age (OR = 1.16, 95% CI [1.05, 1.28]) were associated with increased odds of AD in the BO group. Greater years of education were associated with reduced odds of AD for both BO (OR = 0.91, 95% CI [0.85, 0.98]), and SM (OR = 0.95, 95% CI [0.90, 0.99]), while ever use of HT was associated with decreased odds of AD only for the BO group (OR = 0.43, 95% CI [0.23, 0.82]).Conclusions: Women with early BO, particularly with an APOE4 allele, are at high risk of AD. Women with early BO who use HT and those with increased education have lower odds of developing AD.