Ageing is associated with the appearance of several serum autoantibodies, including thyroid autoantibodies. The biological and clinical significance of this phenomenon is still unknown, since, with the exception of primary myxedema, the prevalence of clinically overt thyroid autoimmune diseases is not increased in the elderly. The peculiar link between autoimmune thyroid failure and ageing is also underscored by the high prevalence of subclinical hypothyroidism in elderly subjects with positive serum thyroid autoantibodies, and could be the consequence of preferential age-dependent expression of destructive effector mechanisms and/or increased target gland susceptibility. Thyroid autoimmunity and subclinical hypothyroidism have also been implicated in the pathogenesis of other age-associated disorders, in particular coronary heart disease. Interestingly, recent data from our laboratories showed that thyroid autoantibodies are rare in healthy centenarians and in other highly selected aged populations, while they are frequently observed in unselected or hospitalized elderly. Taken together, these data suggest that thyroid autoimmune phenomena are not the consequence of the ageing process itself, but rather might be related to age-associated disease.