The relationships between conduct problems and attention deficit behaviors at age 8 years and the use of alcohol, tobacco, and illicit drugs at 15 years were studied in a birth cohort of over 900 New Zealand children. The analysis showed that while early conduct problems were significantly associated with later substance use there were no significant associations between early attention deficit behaviors and later substance use once the correlations between conduct problems and attention deficit behaviors were taken into account. These associations persisted after control for a range of potentially confounding covariates. Children who showed tendencies to conduct problems at age 8 consumed 1.5 to 1.9 times more alcohol and had rates of alcohol-related problems, daily cigarette smoking, and illicit drug use that were 1.9 to 2.0 times higher than children with low conduct problem scores. It is concluded that attention deficit behaviors, in the absence of conduct problems, are not associated with later substance use. However, even when due allowance is made for social and contextual factors associated with both early conduct problems and later substance use, early conduct problems are a risk factor for later substance use.