This double-blind, parallel-group, multicenter study compared the efficacy and safety of intravenous (i.v.) ondansetron with oral syrup ondansetron plus oral dexamethasone in the prevention of nausea and emesis in pediatric patients receiving moderately/highly emetogenic chemotherapy. On each day of chemotherapy, patients were administered ondansetron 5 mg/m2 i.v. and placebo syrup orally (n = 215) or ondansetron 8 mg syrup orally and placebo i.v. (n = 223) plus dexamethasone 2-4 mg p.o. Ondansetron 4 mg syrup p.o. was administered twice daily for 2 days following the cessation of chemotherapy. Complete or major control of emesis was obtained in 89% patients in the i.v. group and 88% patients in the oral syrup group during the worst day of chemotherapy treatment (90% CI: -6, 4) and in 85% and 82% patients, respectively, during the worst day of the study period (90% CI: -8, 3). Intravenous or oral syrup ondansetron plus dexamethasone was well tolerated and effective in preventing chemotherapy-induced emesis in pediatric patients.