Attention-deficit hyperactivity disorder (ADHD) is one of the most-common psychiatric disorders; it is highly comorbid with many other psychiatric disorders and associated with substantial role impairment. Untreated ADHD results in psychiatric comorbidity, relationship and parenting problems, underachievement, frequent job losses, and opportunistic delinquency. Nevertheless, ADHD remains the most under-recognised and undertreated mental health condition in adults. This article discusses the clinical presentation of ADHD in adulthood with a particular focus on recognition, assessment and management of ADHD in adults in primary care.