Previous studies have demonstrated inflammation to be a risk factor in patients with atrial fibrillation (AF). In this prospective study of 90 patients with persistent and permanent AF and 46 controls, we found increased C-reactive protein (CRP) and interleukin-6 levels in patients with AF compared with controls (p <0.001). Multivariate analysis revealed CRP to be an independent predictor of AF (p = 0.01). Left atrial diameter was positively related to CRP and interleukin-6 (p <0.001, R = 0.37; p <0.001, R = 0.46, respectively) and negatively related to left ventricular function. Interleukin-6 levels were positively related to AF duration before cardioversion (p = 0.02). Elevation of CRP and interleukin-6 suggest a role of inflammation in AF, and the relation of CRP and interleukin-6 to left atrial size and AF duration before cardioversion indicates that inflammation may participate in the process of atrial remodeling.