Seven thyroid function parameters (total T3, TT3; total T4, TT4; free T3, FT3; free T4, FT4; TSH; anti-thyroglobulin antibodies, TGAb; and anti-microsomal antibodies, TMAb) were studied in a series of 20 healthy centenarians in order to evaluate their thyroid function status. Our results showed that all the parameters were within normal range, with the exception of TT4 values which were reduced in 60% of centenarians examined. Therefore, the authors believe that the production of thyroid hormones seems to decrease in advanced years, but that this may not solely depend on thyroid parenchyma involution, but also on a lower demand by the hormone sensitive tissues. Centenarians seem to be adapted euthyroid subjects who present low, nonetheless adequate, levels of circulating thyroid hormone (T4).