Objective. To evaluate the incidence and causes of atrial fibrillation (AF), including the components of the metabolic syndrome (MS) in patients with this arrhythmia hospitalized in a therapeutic clinic.Design and methods. We performed a retrospective analysis of 10663 case histories of patients hospitalized in a therapeutic clinic during 5 years (from 2014 to 2018). Diagnostics of MS components was performed according to the criteria of IDF (2005).Results. The incidence of AF in hospitalized patients was 12,3 %. The most common diseases associated with AF were: hypertension (HTN) (92,8 %), coronary artery disease (CAD) (54,9 %), obesity (42,2 %) and diabetes mellitus (DM) (30 %). It was found that the incidence of obesity in patients with AF increased by 10 %, and the proportion of patients with 3 or more components of MS increased by 22,9 % for the period from 2014 to 2018. Asymptomatic arrhythmia was observed in 58,9 % patients with AF. A comparative analysis showed that patients with obesity were more likely to experience multiple AF paroxysms per month as compared to patients without obesity: 43/69 (57,9 %) and 37/89 (46,1 %), p = 0,015. The obesity increased the probability of frequent AF paroxysms by 2,32 times (95 % CI 1,22-4,43). Single AF paroxysms without subsequent relapses were more common in patients without obesity than in patients with obesity: 35/89 (34,8 %) and 15/69 (26,1 %), p = 0,029.Conclusions. The incidence of AF in patients hospitalized in a therapeutic clinic is 12,3 %, and the most common diseases associated with AF are HTN, CAD, obesity and DM. The prevalence of obesity and MS in patients with AF increased in 2018 as compared to 2014.