Cognitive function was examined in 6 patients with genetically confirmed Machado-Joseph disease (MJD) and 15 age- and ethnically matched controls using a series of subtests from the Cambridge Neuropsychological Test Automated Battery (CANTAB), a touch screen-based testing system previously validated in a number of movement and neurodegenerative disorders. The MJD patients had deficits in visual attentional function that were characterized by a slowing of the processing of visual information when task demands were high and an inability to shift attention to previously irrelevant stimulus dimensions to discriminate between complex stimuli. Tests of learning and visual memory were normal. These results demonstrate that specific cognitive deficits occur in patients with MJD, independent of motor dysfunction, and these deficits may reflect disruption to frontosubcortical pathways.