Worldwide, rotavirus is the leading cause of severe acute diarrhea in children aged <5 years. In the United States, before introduction of a live, oral pentavalent rotavirus vaccine (RV5) in 2006, rotavirus caused an estimated 20 to 60 deaths, 55,000 to 70,000 hospitalizations, 205,000 to 272,000 emergency department visits, and 410,000 outpatient visits annually. Before 2000, rotavirus had a predictable winter-spring seasonality and geographic pattern in the United States, with activity beginning in the West census region during December-January, extending across the country, and ending in the Northeast region during May-June. A similar but less pronounced trend was observed during 2000-2006. To characterize trends and compare the 2007-08 and 2008-09 rotavirus seasons with the prevaccine period 2000-2006, CDC analyzed data from the National Respiratory and Enteric Viruses Surveillance System (NREVSS). The results indicated that the 2007-08 and 2008-09 seasons were both shorter and later than the median during 2000-2006. The 2008-09 season had 15% more positive rotavirus test results than the 2007-08 season, but the number of positive test results during each season was substantially lower than the median observed during 2000-2006. Continued surveillance is needed to characterize the effect of routine childhood rotavirus vaccination on rotavirus disease in U.S. children.