Aim. The aim of the study was to assess the prevalence asleep disorders in the preclinical period of the Alzheimer's disease (AD). Method. The initial population consisted of care centers residents, who had had the presence of dementia excluded. The enrolled patients (n = 2910) underwent the assessment of cognitive functions by means of the A DAS-cog scale, as well as of the severity of sleep disorders on the basis of the NPI-NH scale and the AMDP scale. The diagnosis of dementia was verified at the end of the observation period, after seven years, and annually during the follow-up tests. Dementia in the Alzheimer's disease was diagnosed based on the NINCDS-ADRDA criteria. Results. After seven years of observation, 150 patients were qualified to the final analysis. 25 of them were diagnosed to suffer from the AD, while 111 people (forming the control group) did not meet the criteria of dementia. The control group was compared with the AD group in terms of incidence and severity of sleep disorders assessed based on the elements of the NPI-NH scale and the AMDP scale. Disturbances in the assessed categories were more pronounced in the AD group, reaching statistical significance in the qualitative assessment and with regard to the depth of the ascertained disorders. Conclusion. The patients in the preclinical period of dementia experienced sleep disturbances more frequently and with greater intensity, which in combination with other factors may have some prognostic value.