The efficacy of intravenous metoclopramide in controlling vomiting in children after tonsillectomy was determined in a prospective randomized, double-blind investigation. One hundred two unpremedicated, ASA physical status I or II children between the ages of 1 and 15 yr who were undergoing surgical removal of the tonsils, with or without adenoidectomy, were studied. Anesthesia was induced either with halothane, nitrous oxide, and oxygen by mask or by intravenous thiopental and was maintained with halothane, nitrous oxide, oxygen, and intravenous morphine (0.1 mg/kg). Each child randomly received either 0.15 mg/kg of metoclopramide or saline solution placebo intravenously after transfer to the postanesthesia care unit. All episodes of vomiting were recorded for 24 h after completion of surgery. The incidence of vomiting in the saline solution group was 70%, compared with 47% in the metoclopramide group (P = 0.026). The authors conclude that the administration of intravenous metoclopramide in a dose of 0.15 mg/kg on arrival in the postanesthesia care unit significantly decreases the incidence of vomiting in children after tonsillectomy.