SummaryAimsAttention‐deficit with hyperactivity disorder (ADHD) is associated with obesity and impacts the outcome of metabolic and bariatric surgery (MBS). This study aimed at calculating the prevalence in candidates for MBS, which is yet unclear.MethodsWe conducted a systematic review and meta‐analysis, searching three databases from their respective inception to December 2022 for studies reporting the prevalence of ADHD in adolescents and adults assessed before undergoing MBS. The protocol was registered in PROSPERO (CRD42022384914). We adhered to Meta‐analysis of Observational Studies in Epidemiology (MOOSE) and Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) 2020 guidelines; the quality of studies was assessed with the JBI Critical Appraisal checklist. Random‐effect meta‐analyses were performed; confidence intervals were computed with a binomial exact method, and the pooled estimate was calculated after double arcsine transformation.FindingsFourteen studies (24,455 adults) and three studies (299 adolescents) were selected. The quality of studies was moderate to poor; meta‐analyses were performed on subgroups according to the case definition used. The prevalence is 8.94% and 9.90% in adults, and 28.73% in adolescents.ConclusionsADHD is three times more frequent in adults and six times more frequent in adolescents than in the general population. Recommendations are provided to improve the quality of future studies and obtain more reliable estimates of prevalence.