Significant relationships have been noted between age of onset and demographics, clinical characteristics, and cerebral metabolic activity in obsessive-compulsive disorder (OCD). The authors investigated whether patients with early (N=21) and late (N=17) onset OCD differ with respect to neuropsychological functioning. Results revealed that the late onset OCD group obtained poorer scores on measures of executive function and auditory attention than the early onset group. Late onset OCD was also associated with poorer visual memory relative to healthy comparison subjects. These findings suggest that early and late onset OCD may be the result of at least partially differing neurobiological mechanisms.