Background: There is an increasing evidence linking inflammation to some cardiovascular conditions, such as coronary artery disease and hypertension. Similarly, there is emerging data to support the association between inflammation and atrial fibrillation (AF). We also investigated the role of systemic inflammation in different categories of AF. Methods: Eighty five consecutive patients with AF were enrolled in this study. AF was categorized as new onset, chronic (persistent and permanent) and lone. Age- and sex-matched 30 healthy people consisted of control group. Serum level of high sensitive C-reactive protein (hs-CRP) and interleukin-6 (IL-6) was measured. Results: Serum hs-CRP level was higher in overall AF patients than in controls (0.63 +/- 0.57 vs 0.23 +/- 0.1 mg/dL, p= 0.001). Similarly, IL-6 level was also higher in all AF patients compared with controls (29 +/- 36 vs 11.6 +/- 9.7 pg/mL, p= 0.008). In subgroup analysis, hs-CRP and IL-6 levels were significantly higher in both chronic (0.69 +/- 0.62 vs 0.23 +/- 0.1 mg/dL, p= 0.001; 30 +/- 39 vs 11.6 +/- 9.7 pg/mL, p= 0.001, respectively) and new onset AF patients (0.51 +/- 0.46 vs 0.23 +/- 0.1 mg/dL, p= 0.003; 28.4 +/- 31 vs 11.6 +/- 9.7 pg/mL, p= 0.009, respectively) compared with controls. These markers were not different in new onset and chronic AF subgroups. On the other hand, hs-CRP and IL-6 levels tended to be high in lone AF patients (p= 0.06). The presence of AF was an independent factor for hs-CRP (OR= 0.35, 95% CI= 0.1-0.61, p= 0.005) and IL-6 (OR= 17, 95% CI= 1-37, p= 0.037). Conclusions: Our results support that inflammation may have an important role in the AF pathogenesis. (c) 2006 Elsevier Ireland Ltd. All rights reserved.