Stronger associations were observed in those with ≥4 MetS components and in apolipoprotein-E (APOE)-ε4 non-carriers.<h4>Discussion</h4>In this large population-based prospective cohort, MetS was associated with an increased risk of dementia.<h4>Highlights</h4>MetS was associated with a 12% increased risk of incident all-cause dementia. Here, APOE is linked to metabolic syndrome.