Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that develops during childhood and can last into adulthood. Data from the National Center for Health Statistics Rapid Surveys System collected during October-November 2023 were used to estimate the prevalence of ADHD diagnosis and treatment among U.S. adults. In 2023, an estimated 15.5 million U.S. adults (6.0%) had a current ADHD diagnosis based on self-report; approximately one half received the diagnosis at age ≥18 years. Approximately one third of adults with ADHD took a stimulant medication to treat their ADHD in the previous year, 71.5% of whom had difficulty getting their ADHD prescription filled because it was unavailable. Approximately one half of adults with ADHD have ever used telehealth for ADHD-related services. Telehealth might have benefits for persons with ADHD, including helping them access behavioral treatment or medication prescriptions for ADHD. This report provides national estimates of the prevalence and treatment of ADHD among U.S. adults to help guide clinical care and regulatory decision-making for ADHD among U.S. adults.