The growing incidence of dementia in ageing societies is a major concern of health care organizations. Because of its detrimental influence on the mental and functional statuses of elderly people, it leads to increased economic burdens caused by the social and financial needs of patients with dementia and their caregivers. There has been no data concerning the prevalence of dementia in the elderly in the general Polish community so far. The main aim of the study was to assess the prevalence of cognitive impairment suspected of dementia among the Polish elderly and the relationships between cognitive performance and age, gender, place of residence and educational status. The presented data was the result of nationwide, multicentre PolSenior Study conducted from 2007 to 2011 in the Polish elderly population. Cognitive functions were evaluated using Mini-Mental State Examination (MMSE) performed by pre-trained nurses. The result of MMSE lower than 24 points was classified as cognitive impairment suspected of dementia and divided according to its severity into three stages: mild, moderate and severe dementia. The results were analysed in two ways: raw MMSE and MMSE scores after Mungas adjustment (MMSEadj), that is, corrected for age and educational level, and these were compared. To verify the suspicion of dementia an assessment was complemented by an interview of carers for the occurrence and course of memory disorders, treatment of dementia and by functional status assessment. In order to assess the prevalence of suspicion of dementia in the general Polish population, statistical analyses based on weighting were done. The suspicion of dementia on the basis of raw MMSE was made in 20.4% of respondents aged 65years and more, and after Mungas adjustment in 12.1% of older subjects. The prevalence of cognitive impairment grew with increasing age, as well as depending on the educational status of elderly respondents in both types of analyses; raw MMSE and MMSEadj. There was no significant difference in the prevalence of cognitive impairment according to gender in the general population (raw MMSE); however in analyses including MMSEadj results, the suspicion of dementia was made more often among men. Suspicion of dementia based on raw MMSE and MMSEadj results was made significantly more often among men than women at the age of 65-69years, and significantly more often among the oldest women, aged 90years and more. Suspicion of dementia was diagnosed more often in respondents living in rural communities (based on raw MMSE, but not on MMSEadj), which might be related to the differences in their educational status.