AIMS : Older patients with atrial fibrillation (AF) are at risk of adverse outcomes, which is accentuated by comorbidities. We sought to examine the association between morbidity burden and the treatment of older AF patients. METHODS AND RESULTS : Using Danish nationwide registers we included patients ≥70 years of age between 2010 and 2017 at their first hospitalization due to AF. Using multiple logistic regression models we examined the association between morbidity burden and the odds of receiving oral anticoagulants (OACs), anti-arrhythmic drugs (AADs), and rhythm-control procedures (direct current cardioversions and catheter ablations). A total of 48 995 patients were included with a majority of women (54%), with a median age of 80 years [interquartile range (IQR) 75-85], and a median morbidity burden of 2 comorbidities (IQR 1-3). Increasing morbidity burden was associated with decreasing odds of OAC treatment with patients having >5 comorbidities having the lowest odds [odds ratio (OR) 0.38, 95% confidence interval (CI) 0.35-0.42] compared to patients with low morbidity burden (0-1 comorbidities). Having >5 comorbidities were associated with increased odds of AAD treatment (OR 1.90, 95% CI 1.64-2.21) and decreased odds of AF procedures (OR 0.39, 95% CI 0.31-0.48), compared to patients with a low morbidity burden (0-1 comorbidities). Examining morbidity burden continuously revealed similar results. CONCLUSIONS : In older AF patients, multimorbidity was associated with lower odds of receiving OACs and rhythm-control procedures but increased odds of AADs. This presents a clinical conundrum as multimorbid patients potentially benefit the most from treatment with OACs.