Objective: To investigate meta-analytically if the association between ADHD and illicit substance use (ISU) is maintained when controlling for conduct disorder/oppositional-defiant disorder (CD/ODD). Method: A systematic literature review was conducted through Medline from 1980 to 2008. Data extracted and selections made by one author were reviewed by another. Results: Fifteen articles presented odds ratios (ORs) for the development of ISU in individuals with ADHD controlling for CD/ODD. In total, the study covered results for more than 1,000 individuals. The combined OR for studies that included in their analysis exclusively ISU was 1.35 (0.90-2.03), "p" = 0.15, heterogeneity = 55%. Lack of control for socioeconomic status was related with a weaker association between ADHD and ISU. Conclusion: The existing data do not indicate that ADHD increases the risk of ISU beyond the effects of CD/ODD. However, the combination of all existing data is limited in power to detect a small increase in chance. (Contains 1 table, 2 figures, and 1 note.)