High serum phosphorus levels have been linked with vascular calcification and greater cardiovascular morbidity and mortality. We assessed whether serum phosphorus was associated with the atrial fibrillation (AF) incidence in a large community-based cohort in the United States. Our analysis included 14,675 participants (25% black, 45% men) free of AF at baseline (1987 to 1989) and with measurements of fasting serum phosphorus from the Atherosclerosis Risk In Communities (ARIC) study. The incidence of AF was ascertained through the end of 2008 from study visit electrocardiograms, hospitalizations, and death certificates.