Thyroid function tests in eleven cases of Down syndrome Thyroid functions were investigated in 11 cases of Down syndrome confirmed both by clinical and laboratory findings. Mean age of the patients were 3.50+2.75 (1/365-9.0) years. Congenital hypothyroidsm was detected in two the patients (18.2%); anti-thyroid antibodies were detected in another patient with normal thyroid functions (9.1%). Since both Down syndrome and congenital hypothyroidism can present with similar clinical signs and since a higher incidence of abnormal thyroid functions is found in Down syndrome. In patients with Down syndome, it would be useful to perform thyroid function tests immediately after birth, on the sixth and twelfth postnatal months and once a year thereafter. Klinik ve laboratuvar olarak Down sendromu tanısını alan yaş ortalaması 3.50+2.75 (1/365-9) yıl olan 11 olguda tiroid fonksiyonları araştırıldı. İki olguda konjenital hipotiroidi saptandı (%18.2). Ayrıca tiroid fonksiyon testleri normal olan bir olguda antitiroid antikorları pozitif idi (%9.1). Down sendromu ile konjenital hipotiroidinin klinik bulgu¬larının birbirine benzer olması ve Down sendromunda tiroid fonksiyon bozukluğu insi-dansının yüksek bulunması nedeni ile Down sendromlu olgularda doğumda, 6'ncı, 12'nci ve yılda bir kez olmak üzere tiroid fonksiyon testlerinin yapılması çok yararlı olacaktır.