We present a systematic review of the literature on the prevalence, nature, severity, course, and causes of cognitive deficits in patients with occlusive disease of the carotid artery prior to surgery (if surgery was under discussion). Searches were carried out on Medline and Psychlit from 1980 to 1999 using neurovascular and psychological index terms, and papers and books were checked for further references. Studies describing neuropsychological assessment of groups of patients with carotid obstruction were included. Eighteen studies were found. We extracted from the papers data on study design, demographic characteristics of patients, clinical diagnosis, carotid obstruction, cerebral imaging, time interval between ischemic episode and neuropsychological assessment, neuropsychological assessment procedures, integration and interpretation of test performances, and conclusions of authors. Fourteen studies concluded that there are cognitive deficits both in patients with symptomatic and in those with asymptomatic carotid obstruction; four studies denied cognitive impairment. There were no differences in patient characteristics, study design, or neuropsychological assessment procedures between the 14 studies that found deficits and the 4 that did not. There are indications for a mild, diffuse detrimental effect of carotid occlusive disease on cognitive functioning. However, methodological problems prevent a definitive conclusion. Further research is needed to confirm these findings and to ascertain the neurovascular risk factors for and the natural course of cognitive impairment in patients with carotid occlusive disease.