Subclinical thyroid dysfunction is a possible risk factor for cognitive impairment in old age, but results are inconsistent. Aim of the present study was to evaluate the prevalence of thyroid dysfunction among older community-dwelling adults and to see whether thyroid function impacts the cognitive status of the elderly. We included 1750 participants from the Study on Aging and Dementia in Mexico (SADEM). All subjects were evaluated clinically via specific interviews. TSH levels were analyzed by chemiluminescent immunometry assay. We classified participants into five thyroid state groups: (1) normal TSH levels (0.40-4.0 IU/L) were considered euthyroid; (2) Overt hyperthyroidism: TSH 23 pmol/l; (3) Overt hypothyroidism: TSH >4.8 IU/l, FT4