Atrial fibrillation (AF) is the most common cardiac rhythm disturbance and represents a substantial clinical and public health issue. AF, particularly if inappropriately treated, is associated with poor patient outcomes such as heart failure, stroke and even death. Efforts to address the complex causes of AF are required to attenuate future AF-related morbidity, mortality and economic costs. In addition to increasing age, hypertension, diabetes and prevalent cardiac disease, AF is associated with the emergent epidemics of overweight and obesity. The impact of body weight on the risk of AF and the prognosis of AF (CVD and mortality) in the general population has not been completely clarified. Our study aims to evaluate how baseline body weight and BMI and changes in body weight and BMI impact the incidence and prognosis of AF and types of AF in a prospective study based on community data of both sexes from The Tromsø Study.