Background Neutrophil/lymphocyte ratio (NLR) has been proposed as a novel marker of systemic inflammation and oxidative stress. The objective of this study was to ascertain the relationship between levels of NLR and recurrence of lone atrial fibrillation (AF) after catheter ablation. Methods A total of 379 lone AF patients who underwent catheter ablation were enrolled in the study. The NLR before and after catheter ablation was determined. Cox regression analyses were used to estimate the relationship between NLR and the recurrence of lone AF. Results After a mean follow-up of (30.5 +/- 5.3) months, 124 (32.7%) patients had AF recurrences. The patients who developed AF recurrence had a higher postablation NLR (post-NLR) than patients with no recurrence (5.74 +/- 1.55 vs. 4.66 +/- 1.27, P <0.001). Multivariate Cox regression analysis revealed that post-NLR (hazard ratio (HR) 1.514, 95% confidence interval (Cl) 1.364-1.680, P <0.001), left atrium diameter (HR 1.035, 95% Cl 1.001-1.071, P=0.04) and body mass index (HR 1.028, 95% Cl 1.002-1.054, P=0.03) were independent predictors of AF recurrence. Using a cut-off level of 5.15, post-NLR predicted AF recurrence with a sensitivity of 73% and specificity of 67%. Conclusions Our results indicate that an elevated post-NLR is associated with a high rate of lone AF recurrence. A simple measurement of NLR may help us to identify high-risk patients who need pharmacologic intervention to prevent recurrence.