This study has two separate but related purposes: (1) to delineate cross-sectional differences among U.S. high school seniors and young adults that may be due to variations in recent years in state-level minimum drinking age laws and (2) to examine the effects of recent changes in minimum drinking age laws on alcohol consumption and other relevant attitudes and behaviors. Analyses used existing data collected by the Monitoring the Future project, an ongoing study involving annual, nationally representative surveys of high school seniors and annual follow-up surveys by mail of recent graduates. A separate, coordinated study used time-series analyses of official reports to examine effects of increases in the minimum drinking age in several states on rates of fatal crashes. Time-series results were compared with findings from self-report data. The major findings include: higher minimum drinking ages were associated with lower levels of alcohol use among high school seniors and recent high school graduates, even after multivariate controls; lower levels of alcohol use were observed across a number of demographic variables; the lower levels of use persisted into the early 20s, even after all respondents were of legal age; and lowered involvement in alcohol-related fatal crashes among drivers under 21 appeared due to lower alcohol consumption rates--in particular, less drinking in bars or taverns.