Objectives: To describe patterns of and factors associated with antiemetic use among a population-based sample of children with acute gastroenteritis; to determine if filling a prescription for an antiemetic is associated with a significant risk of adverse events; and to determine if filling a prescription for an antiemetic is associated with an increased risk of subsequent health care use. Method and Design: Retrospective cohort study of 20 222 children aged 1, month to 18 years, receiving Medicaid, who had a first diagnosis of gastroenteritis, diarrhea, or vomiting between January 1, 1998, and December 31, 1998. Main Outcome Measures: Presence of a claim for an antiemetic in the 3 days after the initial diagnosis of acute gastroenteritis, subsequent health care usage, and an adverse event within 14 days of the initial diagnosis. Results: Parents of 1802 children (8.9%) with acute gastroenteritis had a prescription for an antiemetic filled within 3 days of the index visit. Factors associated with antiemetic prescription filling for children include older age, provider type (emergency physician, family physician, or general practitioner vs pediatrician), Spanish as the primary language, and rural residency. There was no difference in adverse events between children for whom an antiemetic prescription was filled and for those who did not have an antiemetic prescription filled (odds ratio, 0.68; 95% confidence interval, 0.31-1.46). No difference in risk of subsequent health care use was seen in children who had an antiemetic prescription filled and those who did not (incidence rate ratio, 1.04; 95% confidence interval, 0.94-1.16). Conclusion: Antiemetic use among children with acute gastroenteritis is common and adverse effects seem to be rare.