['Thyroid dysfunction may accelerate atherosclerosis. Aortic pulse wave velocity (PWV) is an early index of arterial stiffness and an important risk factor for cardiovascular disease and might therefore be linked to changes in thyroid activity. We investigated the relationship between thyroid function and carotid-femoral PWV, as an index of arterial stiffness.', 'Cross-sectional cohort study.', 'Participants from the SardiNIA study. Those being treated for thyroid diseases were excluded, yielding a sample of 5875 aged 14-102.', 'Clinical parameters, blood tests including serum TSH and serum FT4, and carotid-femoral PWV were measured.', 'After adjusting for confounders, a direct and linear association between FT4 and PWV was shown (multiple regression analysis). The model containing age, mean blood pressure, body mass index, heart rate, FT4, hypertension, diabetes and dyslipidaemia accounted for 55% of the variation in PWV.'] Are serum free thyroxine levels positively associated with arterial stiffness in the SardiNIA study?