Before rotavirus vaccines were available, rotavirus was the most common cause of severe gastroenteritis in infants and young children in the United States and worldwide. Almost all children were infected by age 5 years. Before vaccine was introduced in the United States, rotavirus was responsible each year for about 3 million episodes of gastroenteritis, 410,000 physician visits, 205,000–272,000 emergency department visits, 55,000–70,000 hospitalizations, and between 20 and 60 deaths among children younger than age 5 years.