The most important side effects of fibrate and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (statin) treatment are hepatic toxicity and myopathy. Obese individuals may have higher levels of serum transaminases than their lean counterparts. The main purpose of this study was to examine the effects of statins and fibrates on liver enzymes in obese patients and to compare them with their effects on patients with various body mass indexes (BMI). Two hundred and sixty-three hyperlipidemic patients of both sexes aged 31-74 years were studied for 24 weeks. One hundred and three patients received fluvastatin (40 mg/day), 62 atorvastatin (10-20 mg/day), 45 micronized fenofibrate (200 mg/day), 44 ciprofibrate (100 mg/day) and nine patients received gemfibrozil (900 mg/day). Laboratory determinations were performed at baseline, after 8 weeks of treatment and at the end of the follow-up period. At baseline, obese patients tended to exhibit elevated liver enzymes more frequently than their lean counterparts (12 of 105 vs. 5 of 67). At the end of the study period, 11 obese, seven overweight and six lean subjects exhibited elevated liver enzymes. Twelve patients who experienced a moderate elevation of serum liver enzymes at baseline had their liver enzyme profile normalized at the end of the study. Furthermore, in 12 patients who had normal serum liver enzyme levels at baseline, abnormal levels of at least one enzyme were observed after 24 weeks of treatment. Fibrates and statins are safe drugs for the treatment of hyperlipidemia in obese patients as well as in those with moderately increased liver enzymes.