With an increase in age, marked changes in thyroid hormone production, metabolism, and action occur. This results in an increased prevalence of (subclinical) thyroid disease in the elderly. In general, subclinical thyroid disease is associated with an increased risk of overt thyroid dysfunction and with different negative clinical parameters. In the elderly, however, it is unclear whether these changes represent physiologic changes in thyroid hormone levels with advancing age or whether they represent true (subclinical) thyroid disease. This review describes the changes in thyroid hormone levels with aging and the mechanisms behind these changes, and also discusses whether subclinical thyroid disease should be treated in the elderly.