This study examined the distribution of substance use, mental health, and criminal behavior among dropouts derived from a nationally representative sample of 18–25 year old (N = 19,312) emerging adults in the United States. Using public-use data from the 2010 National Survey on Drug Use and Health, this study employed multiple logistic regression with adjustments for complex survey sampling and compared high school dropouts with graduates with respect to substance use, mental health, and criminal behavior. After controlling for the effects of age, gender, race/ethnicity, family income, receipt of government assistance, employment status, and metropolitan population density, dropouts were more likely to meet criteria for nicotine dependence and report daily cigarette use, and more likely to report having attempted suicide in the previous year, been arrested for larceny, assault, drug possession or drug sales relative to their high school graduate counterparts. The findings of this study provide important insights and an initial epidemiologic portrait of mental health, substance use, and criminal behaviors of dropouts during emerging adulthood.