Influenza-associated hospitalizations have been a reportable condition in Utah since 2005, and surveillance for influenza hospitalizations has been a valuable tool for identifying and tracking the population impact of serious influenza illness. During the 2009 influenza A (H1N1) pandemic, Utah public health officials used comparisons with hospitalization data from three previous influenza seasons to rapidly assess the impact of 2009 H1N1 and enable public health authorities to target persons at greatest risk for severe illness. This report summarizes the results of that assessment, which determined that 1,327 2009 H1N1 hospitalizations were reported, compared with an average of 435 seasonal influenza hospitalizations during three previous influenza seasons, and 25.5% of 2009 H1N1 hospitalizations resulted in severe illness (intensive-care unit [ICU] admission or death), compared with 14.0% of seasonal influenza hospitalizations. In addition, 2009 H1N1 disproportionately affected racial/ethnic minorities, pregnant women, and residents of Salt Lake County (the state's most densely populated county). During the 4-month "spring wave" of the H1N1 pandemic, a greater percentage of hospitalizations (30.9%) resulted in severe illness than during the 9-month "fall wave" (23.0%). Surveillance for influenza hospitalizations can provide essential data to public health authorities that will help them identify those populations at greatest risk for severe illness.