For a study, researchers sought to evaluate the prevalence and clinical characteristics of atrial fibrillation (AF) in patients of more than or equal to 75 years old and examine the association between AF and hospital length of stay (LOS) and in-hospital mortality. This retrospective investigation focused on patients older than 75 admitted to a secondary hospital in Belgium between January 2017 and December 2019. The complete dataset and a dataset matched by propensity score were subjected to separate survival analyses. Propensity score matching, also known as PSM, was carried out to consider each person’s unique risk of developing AF, given the covariables considered. A total of 3,137 (or 34% of 9,105 patients) were diagnosed with AF upon hospital admission. The prevalence of atrial fibrillation rose with age (29% to 38%) and the Charlson Co-morbidity Index (28% to 57%). Intra-hospital mortality (20%), more patients in the AF group died in the hospital than in the AF-free group (25% vs. 17%, P<0.001). Those without AF had a shorter median LOS was 11, shorter than those without AF (10 [4, 17] days) than those with AF (11 [5, 19] days, P<0.001). After PSM, AF was not related to an increased risk of LOS for more than 10 days (odds ratio 1.08, 95% CI: 0.98 to 1.28, P=0.13). Patients with AF continued to have a greater risk of dying in the hospital than those without AF (log-rank P=0.0015 and hazard ratio 1.17; CI: 1.04 to 1.32, P=0.008). In conclusion, the prevalence of atrial fibrillation (AF) among inpatients older than or equal to 75 years was high (34%) and increased with age and co-morbidity load. After PSM, patients with AF were 17% more likely to die in the hospital than those without AF.