This article describes a comprehensive metaanalysis that was conducted to estimate the prevalence of attention-deficit/hyperactivity disorder (ADHD), as defined by the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). A systematic literature review identified 86 studies of children and adolescents (N0 163,688 individuals) and 11 studies of adults (N014,112 individuals) that met inclusion criteria for the meta-analysis, more than half of which were published after the only previous meta-analysis of the prevalence of ADHD was completed. Although prevalence estimates reported by individual studies varied widely, pooled results suggest that the prevalence of DSM-IV ADHD is similar, whether ADHD is defined by parent ratings, teacher ratings, or a best estimate diagnostic procedure in children and adolescents (5.9-7.1 %), or by self-report measures in young adults (5.0 %). Analyses of diagnostic subtypes indicated that the predominantly inattentive type is the most common subtype in the population, but individuals with the combined type are more likely to be referred for clinical services. Additional research is needed to determine the etiology of the higher prevalence of ADHD in males than females and to clarify whether the prevalence of ADHD varies as a function of socioeconomic status or ethnicity. Finally, there were no significant prevalent differences between countries or regions of the world after controlling for differences in the diagnostic algorithms used to define ADHD. These results provide important support for the diagnostic validity of ADHD, and argue against the hypothesis that ADHD is a cultural construct that is restricted to the United States or any other specific culture.Keywords ADHD . Prevalence . DSM-IV . Subtypes . DiagnosisIn 2007, Polanczyk et al.[1] completed the first comprehensive meta-analysis of the prevalence of attention-deficit/ hyperactivity disorder (ADHD) in children and adolescents. The worldwide prevalence of ADHD was estimated to be 5.29 %, but specific estimates varied widely across the 103 studies included in the analysis. Significant moderators that accounted for a portion of the heterogeneity among studies included the diagnostic criteria used to define ADHD, the method used to assess ADHD symptoms, the specific algorithm used to combine multiple sources of information, and the incorporation of functional impairment as part of the definition of ADHD. Their results also suggested that the prevalence of ADHD was higher in males than females, and highest in young children, but age and gender were not included in final multivariate models, because too few studies reported results stratified on these variables.Interpretation of prevalence studies is complicated by significant changes to the diagnostic criteria for ADHD for the past 30 years, culminating in the current definition specified in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) [2]. The DSM-IV defined 3 nominal subtypes of ADHD, based on differen...