The prevalence of post-stroke dementia (PSD) 3 months after stroke ranges from 6% to 31.8%. PSD includes any type of dementia occurring after stroke but the mechanisms related to its development are still not well identified. Cumulative effect of cerebrovascular lesions, neurodegenerative pathology, white matter changes and aging are consider in development of PSD. One tenth to one sixth of patients admitted to the hospital with stroke already have pre-stroke dementia (Pre-SD). Increasing age is commonly recognized as a risk factor for PSD, but data concerning other factors are inconclusive. Dementia influences the outcome. The aim of this study was: to determine prevalence of Pre-SD, PSD, risk factors for its development and to asses the influence of dementia on early and late prognosis. Pre-SD was evaluated using IQCODE. The patients, who survived, underwent neuropsychological examination during the follow-up visit 3 and 12 months after stroke. The DSM-IV definition for dementia was used. Pre-SD was found in 12% of 250 stroke patients. Female gender history of previous stroke, the number of old infarcts on CT and serum y-globulins level were independently associated with Pre-SD. PSD was diagnosed in 31.4% of stroke survivors at month-3. Factors independently associated with PSD were: increasing age, diabetes mellitus, and more severe neurological deficit on admission. Afte ; r one year dementia was diagnosed in 24% of patients. Factors independently associated with PSD were: increasing age, more severe neurological deficit on admission. Dementia did not influence short and long time prognosis.