This study aimed to estimate the prevalence of adult ADHD and identify its demographic correlates using meta-regression analysis. The researchers searched MEDLINE, PsycLit, and EMBASE databases for relevant publications. The pooled prevalence of adult ADHD was found to be 2.5% (95% CI 2.1–3.1). Gender and mean age, interacting with each other, were significantly related to the prevalence of ADHD. Meta-regression analysis indicated that the proportion of participants with ADHD decreased with age when men and women were equally represented in the sample. The study concluded that the prevalence of ADHD in adults declines with age in the general population, but the unclear validity of DSM-IV diagnostic criteria for this condition may lead to underestimation of the prevalence of adult ADHD.This study aimed to estimate the prevalence of adult ADHD and identify its demographic correlates using meta-regression analysis. The researchers searched MEDLINE, PsycLit, and EMBASE databases for relevant publications. The pooled prevalence of adult ADHD was found to be 2.5% (95% CI 2.1–3.1). Gender and mean age, interacting with each other, were significantly related to the prevalence of ADHD. Meta-regression analysis indicated that the proportion of participants with ADHD decreased with age when men and women were equally represented in the sample. The study concluded that the prevalence of ADHD in adults declines with age in the general population, but the unclear validity of DSM-IV diagnostic criteria for this condition may lead to underestimation of the prevalence of adult ADHD.