The negative side effects of classic antiepileptics, such as Valproate (VPA), often cause patients to discontinue their use. While the negative effects of VPA on lipid profile and thyroid functions have been well published, data regarding the side effects of new antiepileptics, such as levetiracetam (LEV), are not as conclusive. In this study, we investigated the effects of a well-known antiepileptic, VPA, and a new antiepileptic, LEV, on serum lipid levels and thyroid functions in young epileptic patients. Our study included 79 epileptic patients aged between 18-40 years who were undergoing VPA (n=42) or LEV (n=37) monotherapy for at least two years and 58 healthy subjects. Patients with hypertension, diabetes mellitus, thyroid dysfunction, smoking or alcohol addiction, and those who were being treated with any other drugs were excluded from the study. Fasting total cholesterol, LDL-cholesterol, HDL-cholesterol and triglyceride levels were measured for each patient and thyroid function tests were performed. The three groups were compared in terms of these aforementioned parameters. There were no statistical differences in the total cholesterol, LDL-cholesterol, HDL-cholesterol and free-T3 levels between the three groups. The triglyceride levels of the VPA group were significantly higher than those of the LEV and control groups (p=0.0001). While the free-T4 levels of the VPA group were significantly lower than those of the LEV and control groups (p=0.020), TSH levels were higher. The free-T4 and TSH levels did not differ significantly between the LEV and control groups. This study revealed that while the long term use of VPA negatively affected serum triglyceride levels and thyroid functions, LEV did not have any negative effects on these parameters.