Phosphorus levels correlate with atherosclerosis in both animal models and humans with advanced chronic kidney disease, but whether this relationship exists among individuals with normal kidney function is unknown. This study aimed to determine whether an association exists between phosphorus levels and coronary artery calcium levels in a community-based cohort of 3015 healthy young adults in the prospective Coronary Artery Risk Development in Young Adults (CARDIA) study. Phosphorus levels were measured at baseline, and presence of coronary artery calcium was assessed by computed tomography 15 yr later. Mean age at study inception was 25.2 yr, and the mean levels of phosphorus and calcium were 3.6 and 9.5 mg/dl, respectively. Only 0.2% of participants had estimated GFR <60 ml/min per 1.73 m 2. Phosphorus levels were associated with coronary artery calcium in unadjusted models. In multivariate models, however, phosphorus levels were significantly associated with the category of coronary artery calcium level. In conclusion, higher serum phosphorus levels, even within the normal range, may be a risk factor for coronary artery atherosclerosis in healthy young adults.