We measured event-related potentials and reaction times during semantic discrimination tasks in 8 patients with cerebellar degeneration and in 10 normal subjects. The NA, N2 and P3 latencies of patients were significantly longer in patients, whereas N1 and P2 latencies did not differ between both groups. There was also no difference in the simple and GO/NOGO reaction times. These results suggest that these patients' impairment in cognitive information processing arose from a difficulty in pattern recognition of the stimuli represented by the NA component. These data also support the notion that the cerebellum plays a role in cognitive information processing.