Objective: In recent years cohort studies have examined childhood attention-deficit/hyperactivity disorder (ADHD) as a risk factor for substance use disorders (SUDs) in adolescence and young adulthood. The long-term risk is estimated for development of alcohol, cannabis, combined alcohol and psychoactive SUDs, combined SUDs (nonalcohol), and nicotine use disorders in children with ADHD. Method: MEDLINE, CINHAL, PsycINFO, and EMBASE were searched through October 2009; reference lists of included studies were hand-searched. Prospective cohort studies were included if they compared children with ADHD to children without, identified cases using standardized criteria by mean age of 12 years, followed participants until adolescence (nicotine use) or young adulthood (psychoactive substance use disorder, with and without alcohol, alcohol use disorder, cannabis use disorder), and reported SUD outcomes. Two independent reviewers examined articles and extracted and cross-checked data. Effects were summarized as pooled odds ratios (ORs) in a random effects model. Results: Thirteen studies were included. Only two of five meta-analyses, for alcohol use disorder (N = 3,184) and for nicotine use (N = 2,067), estimated ORs showing stability when evaluated by sensitivity analyses. Childhood ADHD was associated with alcohol use disorder by young adulthood (OR = 1.35, 95% confidence interval = 1.11-1.64) and with nicotine use by middle adolescence (OR = 2.36, 95% confidence interval = 1.71-3.27). The association with drug use disorder, nonalcohol (N = 593), was highly influenced by a single study. Conclusions: Childhood ADHD is associated with alcohol and drug use disorders in adulthood and with nicotine use in adolescence. (Contains 1 table and 6 figures.)