Research objective: The aim of this research was to examine whether the severity of inflammation of the supporting tissues of the teeth is a risk factor for the development of mild cognitive impairment in people with untreated periodontitis. Materials and methods: 23 participants, 12 male and 11 female, aged 26 to 60, were included in the research. Informed consent was requested from all participants and anamnestic data as well as oral hygiene habits were recorded. A detailed periodontal status was determined. All of the participants underwent neuropsychological treatment. Results: Everyone had a generalized form of periodontitis, and most of them were diagnosed with stage III. A high index of bleeding on probing (BoP) and the PISA index speak in favor of a large inflammation in the examinee's organism. Almost all of them had a high school education. The median number of years of education was 12.00 (IQR 11.00-15.00), and the median number of teeth was 26.00 (IQR 22.00-29.00). The oral hygiene habits of the majority of respondents were not satisfactory, which was proven by a high plaque index, and 10 of them stated that they smoke tobacco products every day. Of the tested cognitive functions, working memory in auditory form (Digit Span: median=6.00; IQR=5.00-7.00 and Digit Span Reverse test: median=4.00; IQR=4.00- 5.00 ) is statistically significantly worse in relation to the reference values of the healthy European population, as well as mental flexibility and psychomotor speed tested with the Symbol Digit Substitution Test (median=36.00; IQR=27.00-41.00). Linear regression analysis showed that the severity of inflammation of the supporting tissues of the teeth, determined by the PISA index, was not a predictor of MCI, but age and level of education proved to be statistically significant predictors of MCI in people with untreated periodontitis. Conclusion: Older age and lower level of education proved to be risk factors for mild cognitive impairment in people with untreated periodontitis.