To investigate differences in clinical presentation, anticoagulation pattern and outcomes in patients with dementia and atrial fibrillation (AF). A total of 1217 hospitalized patients with non-valvular AF from two institutions were retrospectively evaluated. Diagnosis of dementia was established by a psychiatrist or a neurologist prior to or during hospitalization. Adequacy of warfarin anticoagulation was assessed during follow-up using at least 10 standardized international ratio values. In addition to unmatched comparison, nested case-control study was performed to further evaluate differences in clinical outcomes between patients with and without dementia. A total of 162/1217 (13.3%) patients were diagnosed with dementia. Among other associations, patients with dementia were significantly older with higher number of comorbidities, had lower estimated glomerular filtration rate (eGFR) and lower left ventricular ejection fraction (LVEF), (P < 0.05 for all analyses). Patients with dementia were significantly less likely to receive direct oral anticoagulants (DOACs; 27.2% vs 40.3%; P = 0.001) and were significantly more likely to be inadequately anticoagulated with warfarin (38.9% vs 28.6%; P = 0.008) than patients without dementia. After matching based on age, eGFR, LVEF, and CHA 2 DS 2 -VAS C patients with dementia were significantly more likely to experience inferior overall survival (HR = 1.8; P = 0.001) and shorter time to thrombosis (HR = 2.3; P = 0.019). Our findings speak in support of increased thrombotic and mortality risks in patients with dementia, possibly due to inadequate anticoagulation and higher number of comorbidities.