Dementia cases (<i>n</i> = 614, of which 451 [73.5%] were incident) were recruited at an older age (median 71.3 versus 39.0), were more likely to be male (58.6% versus 44.5%), and were more likely to carry at least one <i>APOE</i> ε4 allele (26.4% versus 19.6%) than controls without dementia (<i>n</i> = 50 490). This evidence concerns the gene APOE and dementia.