The aim of this study was to assess the prevalence of increased thyroid-stimulating hormone (TSH) levels (subclinical or undiagnosed hypothyroidism) in a representative sample of a community-living elderly population and to examine the relationships with cognitive functions and depressive symptoms. An epidemiological study was made of a cohort of 2792 subjects over 65 years of age. A blood sample was obtained from 425 volunteers of this cohort and assayed for TSH. Every subject participating in the study was interviewed and given a battery of neuropsychological tests by a psychologist. Three hundred and eighty-one subjects (89.7%) had normal TSH levels; 18 subjects (4.2%) had TSH lower than 0.4 microU/ml, associated in two of them with hyperthyroxinaemia. Twenty-six subjects (6.1%) had increased TSH levels, associated in 18 of them with a normal free thyroxine level and in eight with a low free thyroxine level. Increased TSH levels were significantly linked with female sex and with the presence of symptoms of depression on the CES-D scale but not with impairment of cognitive function.