We evaluated the effect of dexamethasone on vomiting after elective tonsillectomy in 133 healthy children aged 2-12 yr in a randomized, stratified, blocked, double-blind, placebo-controlled study. General anesthesia was induced by inhalation of N2O and halothane or intravenously (IV) with propofol. Anesthesia was maintained with N2O and halothane. Dexamethasone 150 micrograms/kg up to a maximum dose of 8 mg, or placebo, was administered IV before surgery. All patients received 1.5 mg/kg codeine intramuscularly (IM) intraoperatively. Perioperative IV fluids, management of emesis, postoperative pain and hospital discharge criteria were all standardized. The groups were similar with respect to number, age, weight, length of surgery, and estimated intraoperative blood loss. Dexamethasone reduced the overall incidence of vomiting from 72% (placebo) to 40% (P < 0.001). Vomiting, both in-hospital and postdischarge, was decreased by the prophylactic administration of dexamethasone. Each episode of in-hospital vomiting prolonged discharge by 13 +/- 2 min, mean +/- SD (P < 0.001). In conclusion, dexamethasone markedly decreased vomiting by healthy children after elective tonsillectomy in an ambulatory hospital setting.