Isoniazid, rifampicin, and pyrazinamide, the first-line antituberculosis (anti-TB) drugs, are associated with hepatotoxicity. To study the hepatoprotective effect of N-acetylcysteine (NAC) on liver injury induced by anti-TB drugs. A randomized clinical trial was conducted on 60 new TB patients who were aged 60 years or more. Patients were randomized into two groups. In group I (n=32), drug regimen included daily doses of isoniazid, rifampicin, pyrazinamide, and ethambutol. Patients in group II (n=28) were treated with the same regimen and NAC. The patients were followed up for 2 weeks. Liver enzymes and bilirubins were measured at baseline, after 1 and 2 weeks of treatment, and whenever the patients presented with clinical symptoms of hepatotoxicity. The mean+/-SD values of aspartate aminotransferase and alanine aminotransferase were significantly higher in group I than in group II after 1 and 2 weeks of treatment. Hepatotoxicity occurred in 12 patients with (37.5%) group I and none in group II. The mean duration of treatment before the onset of hepatotoxicity was 4.67+/-4.58 days. NAC protects against anti-TB drug-induced hepatotoxicity.