This study compared earlier temperament and behavioural predictors of opiate misuse and binge drinking, using a sample of high risk young adults. Participants (n=367) are from the Michigan Longitudinal Study, an ongoing community study of children with alcoholic parents and a community contrast sample of families with similarly aged children. We used logistic regression to examine behavioural and temperament factors from ages 15–20 that predicted opiate misuse and weekly binge drinking (five or more drinks on an occasion) in the mid-twenties, controlling for parent alcoholism. At age 24–26, 53 (14.5%) of the participants endorsed misuse of Vicodin and/or OxyContin in the last 3 years. Opiate misuse was predicted by binge drinking, (OR=1.005, p<0.01) and smoking (OR=1.26, p<0.05) in emerging adulthood. Higher reactive control (i.e., the ability to regulate emotions) in emerging adulthood predicted less opiate misuse, when controlling for binge drinking (OR=0.71, p<0.05). In contrast, youth externalising behaviour in mid-adolescence did not predict opiate misuse (OR=1.01, p=0.53), even without controlling for prior binge drinking. At age 24–26, 117 (32% of the sample) endorsed weekly episodes of binge drinking in the previous year. This level of binge drinking was predicted by frequency of binge drinking in late adolescence (OR=1.006, p<0.01). In addition, both reactive control in emerging adulthood (OR=0.56, p<0.001) as well as externalising behaviour (OR=1.05, p<0.05) in mid-adolescence predicted weekly binge drinking. This study shows that temperament factors play a role in the development of opiate misuse, whereas earlier externalising behaviour problems do not act as the same warning signs that they do for alcohol misuse. This understanding can help to target adolescents who are most at risk for developing later opiate misuse.