Atrial fibrillation (AF) recurrences after catheter ablation are common within the first month after AF ablation, and inflammatory processes may be related to AF genesis. This study aimed to clarify the relation between inflammatory processes and recurrence of AF after ablation and to characterize AF recurring within 3 days after ablation (immediate AF recurrence).The study included 186 patients with drug-refractory paroxysmal AF who underwent extensive pulmonary vein isolation. Body temperature and C-reactive protein level were measured before and consecutively on the first 3 days after ablation. Signs of pericarditis or atrial arrhythmias within 3 days after ablation were also monitored. Forty-five patients (24%) had immediate AF recurrence (immediate-AF-recurrence group), 27 (14%) had early recurrence 4 to 30 days after ablation (early-AF-recurrence group), and the remaining 114 (61%) had no AF recurrence within 1 month after ablation (no-AF-recurrence group). Increases in body temperature and C-reactive protein level from baseline in the immediate-AF-recurrence group were the highest among the 3 groups, and signs of pericarditis were observed in 15 of the 45 patients (33%) in the immediate-AF-recurrence group. Atrial premature contractions and nonsustained AF occurred most frequently in the early-AF-recurrence group. After 6-month follow-up, the AF-free rate was greater in the immediate-AF-recurrence group (76%) than in the early-AF-recurrence group (30%). In conclusion, immediate AF recurrence has an apparently different mechanism and impact on midterm outcomes than does early AF recurrence. Acute inflammatory changes after ablation may be responsible for immediate AF recurrence.