Acute gastroenteritis (AGE) is one of the most common reasons for children seeking care in the emergency department (ED), accounting for nearly 2 million visits in the United States each year. For children with AGE and mild to moderate dehydration, oral rehydration therapy (ORT) is effective and recommended by the Centers for Disease Control and Prevention1 and American Academy of Pediatrics as first-line therapy. However, vomiting is common in children with AGE and may prevent the success of ORT. Ondansetron, which became available in generic formulation in 2006, is efficacious in reducing vomiting and the need for intravenous (IV) rehydration and hospital admission,2 but little is known about its effectiveness in real-world practice.