Background The objective of this work was to assess the efficacy of serum eosinophil cationic protein ECP concentration in predicting early postoperative recurrence in patients with chronic rhinosinusitis with nasal polyps CR-SwNP Methods We prospectively enrolled CRSwNP patients to receive bilateral functional endoscopic sinus surgery FESS and followed them for year Serum ECP level was measured within week before surgery Demographics and associated medical factors were analyzed with the surgical outcome and nasal polyp histology was microscopically examined Results Overall patients met the inclusion criteria and underwent FESS A er at least a-year follow-up period patients had postoperative recurrence with significantly higher serum ECP levels p = Receiver operating characteristic curve analysis showed the optimal cutoff level of serum ECP concentration for predicting the postoperative recurrence of nasal polyps was μg/L p = Regardless of atopy status and histology type logistic regression analysis showed that a higher ECP level was the sole significant factor related to early postopera-tive recurrence of nasal polyps odds ratio p = Cox proportional hazard regression analysis revealed that the hazard ratio of CRSwNP patients with an ECP level of > μg/L resulting in early postoperative recurrence was p = Conclusion Serum ECP appears to be a feasible predictor for early postoperative recurrence of nasal polyps CRSwNP patients with preoperative serum ECP levels of ≥ μg/L had an approximately-fold increased risk of early recurrence CRSwNP patients with higher preoperative serum ECP levels should be closely monitored within the first year a er surgery © 2020 ARS-AAOA, LLC.