BACKGROUND: Although it is known that childhood attention-deficit/hyperactivity disorder (ADHD) often persists into adulthood, childhood predictors of this persistence have not been widely studied. METHODS: Childhood history of ADHD and adult ADHD were assessed in 10 countries in the World Health Organization World Mental Health Surveys. Logistic regression analysis was used to study associations of retrospectively reported childhood risk factors with adult persistence among the 629 adult respondents with childhood ADHD. Risk factors included age; sex; childhood ADHD symptom profiles, severity, and treatment; comorbid child/adolescent DSM-IV disorders; childhood family adversities; and child/adolescent exposure to traumatic events. RESULTS: An average of 50% of children with ADHD (range: 32.8%-84.1% across countries) continued to meet DSM-IV criteria for ADHD as adults. Persistence was strongly related to childhood ADHD symptom profile (highest persistence associated with the attentional plus impulsive-hyperactive type, odds ratio [OR]=12.4, compared with the lowest associated with the impulsive-hyperactive type), symptom severity (OR=2.0), comorbid major depressive disorder (MDD; OR=2.2), high comorbidity (>or=3 child/adolescent disorders in addition to ADHD; OR=1.7), paternal (but not maternal) anxiety mood disorder (OR=2.4), and parental antisocial personality disorder (OR=2.2). A multivariate risk profile of these variables significantly predicts persistence of ADHD into adulthood (area under the receiving operator characteristic curve=.76). CONCLUSIONS: A substantial proportion of children with ADHD continue to meet full criteria for ADHD as adults. A multivariate risk index comprising variables that can be assessed in adolescence predicts persistence with good accuracy.