In this study, we aimed to investigate the effects of antiseizure medications on serum thyroid-stimulating hormone (TSH), free thyroxin (fT4) levels, and the frequency of subclinical hypothyroidism in children with epilepsy. One hundred and eighty-one pediatric patients receiving valproate, phenobarbital, carbamazepine, and levetiracetam monotherapy were included. The serum TSH levels were significantly higher at 6th, 12th, and 18th months of the treatment compared with the pre-treatment levels in valproate-treated patients. Serum fT4 levels in carbamazepine group were significantly lower than levetiracetam, valproate, and phenobarbital groups at 12th and 18th months of the treatment. Serum fT4 and TSH levels in levetiracetam group showed no significant changes at any time point. The frequency of subclinical hypothyroidism at 18th month was 16% in valproate, 11% in phenobarbital, 7% in carbamazepine, and 0% in levetiracetam groups. Our data suggest that levetiracetam monotherapy does not cause thyroid dysfunction.