In a population-based cohort of 70,935 adults aged 50 years and older from the Swedish AMORIS study, both absolute and functional iron deficiency were associated with an increased risk of incident dementia over a mean 12.6-year follow-up. Compared with individuals with normal iron measures, absolute iron deficiency and functional iron deficiency were associated with modestly higher dementia risk after adjustment for demographic and clinical factors, with consistent findings across most subgroups and sensitivity analyses.