Attention-deficit/hyperactivity disorder is the most prevalent behavioral disorder in children, and persists into adulthood. Stimulants (methylphenidate and amphetamines) with dopaminergic mechanisms are the most commonly used pharmacological treatment. Nonselective (desipramine and imipramine) and selective (atomoxetine) norepinephrine reuptake inhibitors can also be effective. What constitutes a sufficient response to treatment? Too often a partial response, leaving the patient symptomatic, is accepted. If response is defined more strictly, allowing for a return to normal, then the usually quoted 70% response rates to any given attention-deficit/hyperactivity disorder medicine drop to approximately 40%. With different medicines and not enough patients responding robustly to any given medicine, we can use medicines sequentially to find the medicine that produces a robust response. Alternatively, P300 topography can be used to select optimal treatment.