To assess trends in number of hospitalizations, outcomes, and costs of severe sepsis in the United States. Temporal trends study using the Nationwide Inpatient Sample. Adult patients with severe sepsis (defined as a diagnosis of sepsis and organ dysfunction) diagnosed between 2003 and 2007. We determined the weighted frequency of patients hospitalized with severe sepsis. We calculated age- and sex-adjusted population-based mortality rates for severe sepsis per 100,000 population and also used logistic regression to adjust in-hospital mortality rates for patient characteristics. We calculated inflation-adjusted costs using hospital-specific cost-to-charge ratios. We identified a rapid steady increase in the number of cases of severe sepsis, from 415,280 in 2003 to 711,736 in 2007 (a 71% increase). The total hospital costs for all patients with severe sepsis increased from $15.4 billion in 2003 to $24.3 billion in 2007 (57% increase). The proportion of patients with severe sepsis and only a single organ dysfunction decreased from 51% in 2003 to 45% in 2007 (p < .001), whereas the proportion of patients with three or four or more organ dysfunctions increased 1.19-fold and 1.51-fold, respectively (p < .001). During the same time period, we observed 2% decrease per year in hospital mortality for patients with severe sepsis (p < .001), as well as a slight decrease in the length of stay (9.9 days to 9.2 days; p < .001) and a significant decrease in the geometric mean cost per case of severe sepsis ($20,210 per case in 2003 and $19,330 in 2007; p = .025). The increase in the number of hospitalizations for severe sepsis coupled with declining in-hospital mortality and declining geometric mean cost per case may reflect improvements in care or increases in discharges to skilled nursing facilities; however, these findings more likely represent changes in documentation and hospital coding practices that could bias efforts to conduct national surveillance.