Objective: Anti-epileptic drugs, such as carbamazepine (CBZ) or phenytoin, may induce hypothyroidism in epilepsy patients. We assessed thyroid function of chronic patients with severe motor and intellectual disabilities (SMID) in our hospital. Methods: We examined thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free thyronine (fT3) in 73 patients with SMID (47 men and 26 women, average age 48.4 years, range 30-68 years) without thyroid hormone supplement therapy. We determined the relationship between the thyroid function of patients taking the anti-epileptic drugs CBZ, valproate (VPA), and phenobarbital, other medications including anti-psychotic drugs, and treatments without anti-epileptic or anti-psychotic drugs. Results: TSH levels were not significantly different between the groups taking CBZ (CBZ+med), other anti-epileptic drugs or anti-psychotic drugs (CBZ-med), and only medications without anti-epileptic or anti-psychotic drugs (Non-med). The CBZ+med group had significantly lower fT4 levels than the CBZ-med or Non-med groups. There was a negative correlation between thyroid function level and the phenobarbital groups. TSH levels of the VPA+med group were significantly higher than VPA-med and Non-med group; fT3 and fT4 levels were not significantly different. Conclusions: Our results indicate that hypothyroidism may be present in patients with SMID taking anti-epileptic drugs. This suggests it is important to regularly measure thyroid function in patients with SMID taking anti-epileptic drugs, especially CBZ.