BACKGROUND: There is systematic variation between hospitals in their care of severe sepsis, but little information on whether this variation impacts sepsis-related mortality, or how hospitals' and health-systems' impacts have changed over time. OBJECTIVE: To examine whether hospital and regional organization of severe sepsis care is associated with meaningful differences in 30-day mortality in a large integrated health care system, and to examine the extent to which those effects are stable over time. METHODS: Retrospective analysis of 43,733 patients with severe sepsis in 114 hospitals and 21 geographic regions in the United States Department of Veterans Affairs in 2012, compared to 33,095 such patients in 2008. We used risk- and reliability-adjusted hierarchical logistic regression to estimate hospital- and region-level random effects after controlling for severity of illness using a rich mix of administrative and clinical laboratory data. RESULTS: The median hospital in the worst quintile of performers had a risk-adjusted 30-day mortality of 16.7% (95% CI: 13.5%, 20.5%) in 2012, compared to the best quintile, which had a risk-adjusted mortality of 12.8% (95% CI: 10.7%, 15.3%). Hospitals and regions explained a statistically and clinically significant proportion of the variation in patient outcomes. 30-day mortality after severe sepsis declined from 18.3% in 2008 to 14.7% in 2012 despite very similar severity of illness between years. The proportion of the variance in sepsis-related mortality explained by hospitals and regions was stable between 2008 and 2012. CONCLUSIONS: In this large integrated healthcare system, there is clinically significant variation in sepsis-related mortality associated with hospitals and regions. The proportion of variance explained by hospitals and regions has been stable over time, although sepsis-related mortality has declined.