More than one quarter of high school students begin drinking alcohol before the age of 13 years. Early onset of alcohol use is associated with many problems, both in adolescents and adults, including risk of injury, risk of unwanted and unprotected sex, other substance abuse, and school failure. This survey of 43 000 adults found that those who began drinking before the age of 14 years have nearly double the risk of alcohol dependence compared with those who started drinking after the age of 21 years. They were also 3 times more likely to have multiple episodes of alcohol dependence. For each additional year before the age of 21 years that individuals began drinking, the odds of developing alcohol dependence problems increased.