Attention-deficit hyperactivity disorder (ADHD) is a persistent, pervasive disorder characterised by symptoms of inattention, impulsivity and hyperactivity. Although traditionally considered a disorder of childhood, symptoms and associated impairments persist into adulthood for a significant proportion of individuals. Untreated ADHD can have a number of adverse effects for both the individual and wider society. Despite this, ADHD in adults is often misdiagnosed or its diagnosis is ‘missed’ in general psychiatric settings and this article highlights some reasons for this.