There is growing evidence for neuropsychological dysfunction in obsessive-compulsive disorder (OCD) related to an underlying frontal lobe and/or basal ganglia dysfunction. The following paper is a systematical review of the existing literature on cognitive impairment in OCD patients. Fifty studies were surveyed with regard to methodological aspects and cognitive impairments found in OCD patients. In addition, the impact of confounding variables such as psychotropic medication, co-morbidity or severity of symptoms on neuropsychological functioning as well as effects of treatment are discussed. OCD is often related to memory dysfunction that seems to be associated with impaired organization of information at the stage of encoding. Several other executive functions are also commonly disturbed, though results are inconsistent. The results of our study suggest that some cognitive deficits seem to be common in OCD, but future studies should focus more on possible confounding variables such as co-morbidity or psychotropic medication.