Rotavirus (RV) has a characteristic seasonal pattern in the 48 contiguous states of the continental United States, and climatologic factors have been implicated though not confirmed. Since 1997, three significant events occurred, including strong El Niño and La Niña climatologic phenomena, and the brief introduction of a rotavirus (RV) vaccine. We examined trends in RV activity in the continental United States between 1997 and 2004, using data from a network of over 70 laboratories that voluntarily report weekly RV detection rates within the National Respiratory and Enteric Virus Surveillance System (NREVSS). Analysis of NREVSS data indicates characteristic winter activity that begins in the Southwest in December or January, moves across the country, and ends in the Northeast in April or May. This pattern was not affected by the brief use of RV vaccine nor by periods of climate change associated with the El Niño and La Niña phenomena. The temporal and geographic pattern of RV spread in the United States has persisted since its initial description and defies easy explanation. An impact of the RV vaccine was not observed, either because of the limited uptake of the vaccine or the inherent variability of the system. NRVESS permits a gross assessment of RV geographic and temporal trends in the United States, but underscores the need for additional assessment mechanisms.