BACKGROUND: Since 1995, 14 states have passed laws encouraging or mandating influenza vaccination for hospital workers. Although the Centers for Disease Control and Prevention recommends vaccinating health care workers to reduce disease transmission and patient risk, the effect of these laws on pneumonia and influenza mortality is unknown. OBJECTIVE: To measure the effect of state-level hospital worker influenza vaccination laws on pneumonia and influenza mortality. DESIGN: Quasi-experimental observational study. SETTING: United States. PARTICIPANTS: Population of all states from 1995 to 2017. INTERVENTION: State adoption of a law promoting influenza vaccination for hospital workers. MEASUREMENTS: Pneumonia and influenza mortality per 100 000 persons by state and by month, both population-wide and separately by age group, obtained from restricted-access National Vital Statistics System files. Linear and log-linear models were used to compare changes in mortality rates for adopting versus nonadopting states. RESULTS: Implementation of state laws requiring hospitals to offer influenza vaccination to their employees was associated with a 2.5% reduction in the monthly pneumonia and influenza mortality rate (-0.16 deaths per 100 000 persons [95% CI, -0.29 to -0.02]; P = 0.022) during the years when the vaccine was well matched to the circulating strains. The largest effects occurred among elderly persons and during peak influenza months. LIMITATION: Utilization of large-scale national data precluded analysis of more specific outcomes, such as laboratory-confirmed or hospital-acquired influenza. CONCLUSION: State laws promoting hospital worker vaccination against influenza may be effective in preventing pneumonia- and influenza-related deaths, particularly among elderly persons. Vaccinating hospital workers may substantially reduce the spread of influenza and protect the most vulnerable populations.None.