background: data on the prevalence of primitive reflexes (pr) in adulthood, their pathological significance and relationship to age and cognition are controversial. objective: to study the relationship between pr and cognition in 30 patients with probable alzheimer's disease (ad) and 154 control subjects. method: diagnosis of probable ad was based on dsm-iv, nincds-adrda, and camdex criteria. primitive reflexes were quantified from zero (absent) to 1 (mild) or 2 (markedly present). the cognitive abilities screening instrument - short form (casi-s) was used to evaluate registration, temporal orientation, verbal fluency and recall. a drawing test was added. results: most frequent pr among demented and controls were suck (77% and 62%, respectively) and snout (60% and 27%), followed by glabellar (30% and 19%), paratonia (37% and 5%), and palmomental (23% and 5%). none of controls had more than three pr. frequency of pr tended to increase with age and cognitive deterioration. grasp and babinski responses were found only in dementia patients. primitive reflexes were not correlated with each other, except snout with suck, and snout with glabellar reflex. conclusion: the finding of grasp and babinski sign, or the presence of more than three primitive signs, particularly the combination of paratonia, snout, suck, and palmomental reflexes strongly suggests brain dysfunction, especially when these signs are marked and accompanied by deficits in orientation, recall, verbal fluency, and constructional praxis.