Antituberculosis drug-induced hepatitis attributed to isoniazid (INH) is one of the most prevalent drug-induced liver injuries. INH is metabolized by hepatic N-acetyltransferase (NAT) and cytochrome P450 2E1 (CYP2E1) to form hepatotoxins. The aim of this study was to evaluate whether polymorphisms of the NAT2 and/or CYP2E1 genes were associated with antituberculosis drug-induced hepatotoxicity in Korean patients. A total of 132 patients with tuberculosis who received antituberculosis treatment were followed prospectively. Their NAT2 and CYP2E1 genotypes were determined using polymerase chain reaction (PCR) with or without sequencing. Eighteen (13.6%) patients developed antituberculosis drug-induced hepatotoxicity. Regarding NAT2, slow acetylators had a higher incidence of hepatotoxicity than rapid acetylators (36.8% vs. 9.7%, P=0.005) and there was a 3.8-fold risk of hepatotoxicity for the slow acetylators compared to the rapid acetylators. For the CYP2E1 gene, the RsaI polymorphism in the 5' untranslated region, and a polymorphic repetitive sequence at the CYP2E1 5'-flaking region were analyzed; there was no significant association between any CYP2E1 genotype and antituberculosis drug-induced hepatotoxicity. In conclusion, slow acetylator status of NAT2 was a significant susceptibility risk factor for antituberculosis drug-induced hepatotoxicity; NAT2 genotyping may be a useful tool for predicting antituberculosis drug-induced hepatotoxicity.