Although first identified in children in the 19th century, attention-deficit/hyperactivity disorder (ADHD) in adults was not described in the literature until 1976. The symptoms of adult ADHD resemble the symptoms of childhood ADHD, but symptom intensity, especially hyperactivity, may decrease over time. However, due to the challenges and responsibilities of adulthood, a normal day is extremely complicated for the ADHD adult. Molecular genetics and neuroimaging studies confirm that ADHD is a heterogeneous, neurobiological disorder, mainly of dopaminergic and noradrenergic pathways. Trials of pharmacologic treatments in adults with ADHD have produced mixed results due to considerable variability in diagnostic criteria, dosing, and response. This article reviews the history, neurobiology, and pharmacologic management of adult ADHD.