OBJECTIVE To examine the relationship between age of drinking onset and patterns of use, abuse of other substances, and the prevalence of other alcohol-related problems in a population of midwestern high school seniors. METHODS We analyzed self-report survey data on public school students' history of alcohol and other drug use and related problems from the Minnesota Student Survey conducted in 1989. The sample consisted of 2,650 male and female seniors, representing a 10% random sample of all white seniors in the study. RESULTS The findings suggest that early onset of alcohol use (by age 12) is associated with subsequent abuse of alcohol and related problem behaviors in later adolescence, including alcohol-related violence, injuries, drinking and driving, and absenteeism from school or work, as well as increased risks for using other drugs. CONCLUSIONS This paper identifies the preadolescent years from age 10 to 12 as a particularly vulnerable period for the development of early alcohol dependence and abuse. Delaying alcohol use onset to age 13 may significantly reduce the risk of severe alcohol abuse in later adolescence.