Introduction. Metabolic syndrome (MS) and obstructive sleep apnea (OSA) have some common risk factors, but their combined effect on cognitive function in elderly patients has not been sufficiently studied, which determines the relevance of the study. Objective: to evaluate the effect of obstructive sleep apnea on cognitive functions in elderly patients with metabolic syndrome. Materials and methods. 96 elderly patients with MS were examined, 2 groups were formed: group 1 (n=58 people) - MS and OSA (0-1st) and group 2 (n=38 people) - MS and OSA (2-3rd). A subjective assessment of cognitive complaints (difficulties with memory, concentration, orientation, and daily activities) was conducted using the McNair and Kahn questionnaire (The Cognitive Difficulties Scale), recommended for people over 50 years of age. Objective screening assessment of cognitive status to detect moderate cognitive impairment was performed using the Montreal Cognitive Function Assessment Scale (MoCA). The Stroop test was used to study information processing speed and cognitive control. The statistical analysis was performed in the StatTech v.4.9.5 program (Russia). Results. Elderly patients with MS and concomitant OSA showed a significant deterioration in cognitive functions compared with the MS group without CCA. Mild cognitive impairment (according to the MoCA scale) was diagnosed in 81.6% of patients with OSA (vs 13.9%; p