Geriatric patients (age >65) comprise a growing segment of the trauma population. New-onset atrial fibrillation may occur after injury, complicating clinical management and resulting in significant morbidity and mortality. This study was undertaken to identify clinical and demographic factors associated with new-onset atrial fibrillation among geriatric trauma patients . Methods: In this case control study, eligible participants included admitted trauma patients age 65 and older who developed new-onset atrial fibrillation during the hospitalization. Controls were admitted trauma patients who were matched for age and injury severity score, who did not develop atrial fibrillation. We evaluated the associations between new-onset atrial fibrillation and clinical characteristics, including patient demographics, health behaviors, chronic medical conditions, and course of care. Results: Data were available for 63 cases and 25 controls. Patients who developed atrial fibrillation were more likely to be male, compared to controls (49% versus 24%; odds ratio 3.0[1.0, 8.9]). Other demographic and clinical factors were not associated with new-onset atrial fibrillation, including mechanism of injury, co-morbid medical conditions, drug or alcohol use, surgical procedures, and intravenous fluid administration. Conclusions: Male geriatric trauma patients were at higher risk for developing new-onset atrial fibrillation. Other demographic and clinical factors were not associated with new-onset atrial fibrillation. Competing Interests: The authors report no conflicts of interest.