For those with a clinical diagnosis of dementia, APOE genotype, multimorbidity, early-onset epilepsy, and dementia medication status were all significantly independently associated with mortality, such that presence of 1 or more APOE ε4 alleles, 2 or more health conditions, or early-onset epilepsy each were associated with increased mortality risk, and taking antidementia medication was associated with decreased risk. This evidence concerns the gene APOE and epilepsy, early-onset.