As neuropsychological mechanisms for attention have been hypothesized to be located in the right hemisphere of the brain, several investigators have begun to conceptualize attention deficit hyperactivity disorder (ADHD)-related attentional deficits as involving right-hemispheric abnormalities. The authors evaluated and compared adult patients diagnosed with ADHD with a non-ADHD group of patients using a chronometric visual-spatial attention task that is sensitive to hemispheric differences in efficiency of information processing. Reaction times across different cuing conditions, cue-target delays, and visual fields were assessed. When participants' attention was misdirected with cues in the right visual field and attention had to be switched to a target on the left visual field, there was a longer delay among ADHD adults than non-ADHD adults, specifically when the interval between the cue and target was 800 ms as compared with 100 ms. This specific pattern of dysfunction was interpreted as a difficulty with maintaining attention possibly associated with anterior attention mechanisms in the right hemisphere.