Competing hypotheses stating that past genocide exposure reduces (owing to resilience) versus increases (owing to vulnerabilities) the risk of dementia are yet to receive empirical support. This study tested these competing hypotheses. Registry data were extracted on 51,752 Israeli residents without dementia from September 2002 to January 2012; individuals were born between 1901 and 1945, alive on January 2012, and followed-up for the risk of dementia between January 2013 and October 2017. Groups were classified as exposed to the European Holocaust, based on government recognition, or unexposed. Hazard ratios (HRs) from Cox regression models were used to quantify the risk of dementia between the groups, adjusting for demographic and diagnostic covariates; additionally, 12 sensitivity analyses were computed. In total 10,780 participants (20.8%) were exposed to the Holocaust and 5,584 (10.8%) were diagnosed with dementia during follow-up. Dementia rates were 16.5% in the Holocaust-exposed group and 9.3% in the unexposed group. In the primary analysis, the estimated unadjusted HR of dementia for the exposed compared to the unexposed group was 1.77, 95% CI [1.67, 1.87], and the adjusted HR was 1.21, 95% CI [1.15, 1.28]. Sensitivity analyses significantly replicated the primary results with similar point estimates, adjusted HRs = 1.18-1.28, all ps < .001; all HRs had a small effect size. The current study results are consistent with the hypothesis that exposure to the extreme adversities of genocide heightens vulnerability to the risk of dementia in later life.