e19508 Background: With the increased use of novel agents like Bruton tyrosine kinase inhibitors (BTKi) for the treatment of chronic lymphocytic leukemia (CLL), the incidence of atrial fibrillation (AF) is on the rise in these patients. However, the excess burden added by AF to the morbidity and mortality of CLL patients is unclear. Methods: Using the appropriate ICD-9 and ICD-10 codes, the National Inpatient Sample (NIS) database was accessed to gather data of hospitalized CLL patients with AF from 2008 to 2019. Propensity-score matching (PSM) and logistic regression model were performed to control for baseline patient factors like age, sex, income, and the relevant co-morbidities to match 7265 CLL patient admissions with AF and 7265 CLL patient admissions without AF. The primary outcome was all-cause mortality (ACM), while secondary outcomes included stroke, acute heart failure (AHF), and total cost of hospital stay. Results: The mean age of the cohorts was 82 years. Females made up 44% of both groups. The AF group had similar prevalence of systemic hypertension (62.38% vs 62.10%; p= 0.73), diabetes mellitus (5.09% vs 5.43%; p= 0.35), congestive heart failure (5.57% vs 5.36%; p= 0.58), valvular heart disease (1.17% vs 1.44%; p= 0.14), and pulmonary hypertension (0.21% vs 0.14%; p= 0.31) compared to the group without AF. PSM revealed CLL patients with AF had a higher rate of ACM (6.06% vs 4.47%; p= <0.0001), AHF (7.50% vs 3.85%; p= <0.001), and stroke (3.09% vs 1.65%; p= <0.0001). Admission in the AF group also had a higher median total cost of hospital stay ($9097 vs $7646). A logistic regression model was done to adjust for confounders which revealed similar results for the AF group with increased adjusted odd’s ratio (aOR) of ACM (aOR:1.39, 95% confidence interval (CI): 1.19-1.61; p= <0.001), AHF (aOR: 2.16, 95% CI: 1.85-2.52; p= <0.001), and stroke (aOR:1.94, 95% CI: 1.54-2.44; P= <0.001) (Table). Conclusions: Our data suggest that hospitalized CLL patients with AF are at a significantly increased risk of all-cause mortality, AHF, and stroke. Several limitations like the inability to establish the temporal relationship between CLL and AF and the lack of data regarding medications of individual patients are important to keep in mind while interpreting the results.[Table: see text]