Respiratory syncytial virus (RSV) is the leading cause of pneumonia and bronchiolitis in infants and children. Immune prophylaxis can reduce the risk of severe RSV disease among some high-risk infants. A summary and update of analyses using National Respiratory and Enteric Virus Surveillance System (NREVSS) data is provided to explore using surveillance data to better define the timing of RSV activity and RSV immune prophylaxis. The methodology used was that outlined in a study by Mullins et al (Pediatr Infect Dis J. 2003;22:857-862), which analyzed weekly antigen detection data reported by laboratories to NREVSS. Data reported to NREVSS between 1990 and 2006 were used to assess seasonality among regional, state, and local areas. Season onset, offset, and duration were calculated for each year and each laboratory, and compared with the U.S. Census region and national median measurements. Results demonstrated a distinct winter peak of RSV activity each year. The extent of variation in the timing of RSV activity in a community from year to year makes it difficult to predict the timing of RSV outbreaks. In addition, the onset timing can vary between communities, even those in close proximity, during the same year. There are, however, regional community patterns that may help guide timing of immune prophylaxis. For example, the South region exhibited an earlier median season onset and longer duration than the other regions, with median onset week 47 and duration 16 weeks. In contrast, the Midwest exhibited a significantly later median onset and shorter duration than the other regions, with median onset week 1 of the following year and duration 13 weeks. Therefore, analyses of NREVSS data show that using surveillance data to tailor the timing of immune prophylaxis precisely will be difficult. Surveillance data can, however, be used to determine how well national patterns represent local patterns. Further analyses are needed to determine how local surveillance data can be used to guide timing of immune prophylaxis.