We compared the clinical course of pediatric patients (n = 25) with acetaminophen poisoning treated with an investigational intravenous preparation of N-acetylcysteine (IV-NAC) with that of historical control subjects (n = 29) treated with conventional oral NAC (O-NAC) therapy. Patients received IV-NAC for 52 hours; historical control subjects received O-NAC (72 hours). There were no significant intergroup differences between treatment groups in age (15.5 vs 15.9 years), gender (88% vs 90% female) or distribution of risk categories (probable risk, 12 vs 15; high risk; 13 vs 14). The peak prothrombin time was significantly higher in the IV-NAC group (14.2 vs 13.6 seconds; p = 0.048). Mean treatment delay was significantly longer in the IV-NAC group (14.4 vs 10.4 hours; p = 0.001). Hepatoxicity was noted in two (8.0%) patients in the IV-NAC treatment group and two (6.9%) patients in the O-NAC group. All patients recovered. Our results indicate that 52 hours of intravenous NAC is as effective as 72 hours of oral NAC.