Attention-Deficit Hyperactivity Disorder (ADHD) is a common, genetically transmitted neurological disorder, with onset in childhood, probably mediated by decreased brain dopaminergic functioning. The first author was one of the earliest to describe the persistence of symptoms into adulthood. Prevalence and natural history data suggest that of the 3 to 10% of children diagnosed with ADHD, one- to two-thirds (somewhere between 1 and 6% of the general population) continue to manifest appreciable ADHD symptoms into adult life. This paper describes how ADHD in adults can be readily diagnosed and treated, despite resembling or coexisting with other psychiatric disorders. The Wender Utah diagnostic criteria address adult characteristics of the disorder. Informant and patient interviews and rating scales are used to determine the psychiatric status of the patient as a child, make a retroactive diagnosis of childhood ADHD, and establish the current diagnosis of the adult. Stringent diagnosis is key to determining effective treatment. Dopamine agonist stimulant medications appear to be the most effective in treating ADHD. About 60% of patients receiving stimulant medication showed moderate-to-marked improvement, as compared with 10% of those receiving placebo. The core symptoms of hyperactivity, inattention, mood lability, temper, disorganization, stress sensitivity, and impulsivity have been shown to respond to treatment with stimulant medications. Non-dopaminergic medications, such as the tricyclic antidepressants and SSRIs have generally not been useful in adults with ADHD in the absence of depression or dysthymia. Pemoline is no longer approved for use in these patients, despite early favorable reports. Appropriate management of adult patients with ADHD is multimodal. Psychoeducation, counseling, supportive problem-directed therapy, behavioral intervention, coaching, cognitive remediation, and couples and family therapy are useful adjuncts to medication management. Concurrent supportive psychosocial treatment or polypharmacy may be useful in treating the adult with comorbid ADHD.