Thyroid involvement in Williams syndrome (WS) was recently reported in two small 
groups of patients, both showing an increased prevalence of elevation of TSH 
serum concentration; in one of the two reports, 70% of the patients demonstrated 
a hypoplasia of thyroid gland as well. In our institution, we currently follow a 
large population of WS patients who periodically undergo a multispecialist 
clinical evaluation that includes ultrasound evaluation of the thyroid gland, 
and levels of FT3, FT4, TSH, and anti-thyroid antibodies. Here, we report on the 
prevalence of thyroid structural and functional anomalies, in a population of 95 
WS patients, half of them followed for more than 5 years. Our study confirms the 
increased incidence of both elevated TSH serum values (37.9% in our sample) and 
thyroid gland hypoplasia (74.7%). Moreover, we demonstrated that TSH elevation 
declines with age. For this reason, we suggest that a complete thyroid 
evaluation be performed in every patient with WS, and that this medical 
complication should be periodically searched for in follow-up visits.