Objective To explore associations of state retail alcohol monopolies with underage drinking and alcohol-impaired driving deaths. Data Surveys on youth who drank alcohol and binge-drank recently and their beverage choices; census of motor vehicle fatalities by driver blood alcohol level. Methods Regressions estimated associations of monopolies with under-21 drinking, binge drinking, alcohol-impaired driving deaths, and odds a driver under 21 who died was alcohol-positive. Results About 93.8% of those ages 12–20 who consumed alcohol in the past month drank some wine or spirits. In states with a retail monopoly over spirits or wine and spirits, an average of 14.5% fewer high school students reported drinking alcohol in the past 30 days and 16.7% fewer reported binge drinking in the past 30 days than high school students in non-monopoly states. Monopolies over both wine and spirits were associated with larger consumption reductions than monopolies over spirits only. Lower consumption rates in monopoly states, in turn, were associated with a 9.3% lower alcohol-impaired driving death rate under age 21 in monopoly states versus non-monopoly states. Alcohol monopolies may prevent 45 impaired driving deaths annually. Conclusions Continuing existing retail alcohol monopolies should help control underage drinking and associated harms.