A previously conducted positron emission tomography (PET) study of normal humans suggested that the cerebellum makes important non-motor contributions to language processing. Beginning with the task which produced right cerebellar PET activation, we studied a 49-yr-old male (RC1) with right cerebellar damage on a variety of tasks involving complex non-motor processing. Whereas RC1's performance on standard tests of memory, intelligence, 'frontal function' and language skills was excellent, he had profound deficits in two areas: (1) practice-related learning; (2) detection of errors. Considered in relation to cerebellar contributions to motor tasks, the results suggest some functions performed by the cerebellum may be generalized beyond a purely motor domain.