PURPOSE: It is known that serum thyroid hormones and lipid profiles are affected by the different biotransformation pathways of antiepileptic drugs (AEDs). The aim of this study was to evaluate thyroid functions and lipids in epileptic patients taking AEDs. METHODS: We prospectively examined serum thyroid hormone concentrations and lipid profiles in 45 patients with epilepsy and compared them with 45 healthy age- and sex-matched controls. We measured serum free T4 (FT4), thyroid stimulating hormone (TSH), thyroid peroxidase antibody (TPO-ab), thyroid globulin antibody (TG-ab), total cholesterol, low density lipoprotein (LDL), high density lipoprotein (HDL) and triglycerides (TG). To analyze, the patient groups were divided into two groups:36 patients using hepatic enzyme inducing AEDs and 9 patients using non-enzyme-inducing AEDs. RESULTS: Mean age, sex and body mass index (BMI) were not different in both groups. The serum free T4 level of all patients was lower than that of the control group (p<0.05). The serum free T4 level of the patients taking hepatic enzyme inducing AEDs was lower than that of the control group. TSH, TPO-ab and TG-ab levels were not different in both groups. There was no correlation between free T4 levels and the duration of therapy in the patient group. For lipids, LDL, HDL, TG and total cholesterol, levels were not different in both groups. CONCLUSIONS: Hepatic enzyme inducing AEDs led to a decrease in free T4 levels but the TSH level remained normal. These findings seem to be not only due to liver enzyme induction but also hypothalamic interference of regulation of thyroid hormone production by the drugs. Lipid profiles were not significantly influenced by AEDs but further evaluation should be needed.