BACKGROUND: Although rapid response teams have been widely promoted as a strategy to reduce unexpected hospital deaths, most studies of rapid response teams have not adjusted for secular trends in mortality before their implementation. We examined whether implementation of a rapid response team was associated with a reduction in hospital mortality after accounting for preimplementation mortality trends. METHODS: Among 56 hospitals in Get With The Guidelines-Resuscitation linked to Medicare, we calculated the annual rates of case mix–adjusted mortality for each hospital during 2000 to 2014. We constructed a hierarchical log-binomial regression model of mortality over time (calendar-year), incorporating terms to capture the effect of rapid response teams, to determine whether implementation of rapid response teams was associated with reduction in hospital mortality that was larger than expected based on preimplementation trends, while adjusting for hospital case mix index. RESULTS: The median annual number of Medicare admissions was 5214 (range, 408–18398). The median duration of preimplementation and postimplementation period was 7.6 years (≈2.5 million admissions) and 7.2 years (≈2.6 million admissions), respectively. Hospital mortality was decreasing by 2.7% annually during the preimplementation period. Implementation of rapid response teams was not associated with a change in mortality during the initial year (relative risk for model intercept, 0.98 [95% CI, 0.94–1.02]; P=0.30) or in the mortality trend (relative risk for model slope, 1.01 per year [95% CI, 0.99–1.02]; P=0.30). Among individual hospitals, implementation of a rapid response team was associated with a lower-than-expected mortality at only 4 (7.1%) and higher-than-expected mortality at 2 (3.7%) hospitals. CONCLUSIONS: Among a large and diverse sample of US hospitals, we did not find implementation of rapid response teams to be associated with reduction in hospital mortality. Studies are needed to understand best practices for rapid response team implementation, to ensure that hospital investment in these teams improves patient outcomes.