Nodal factors are important predictors of prognosis for papillary thyroid carcinoma (PTC), but their synergy effect is not well understood. We aimed to explore their synergy effect in predicting recurrence of clinical N1b PTC.Patients who underwent surgery for cN1b PTC from 2013 to 2017 were enrolled. The association between nodal factors and recurrence was assessed using Cox proportional hazards regression models. Interaction and stratified analyses were conducted according to significant nodal factors.Of 1067 cN1b PTC patients included, all nodal factors (bilateral metastasis, largest dimension>3cm, micro and gross extranodal extension (mENE, gENE), No. of metastatic lymph nodes (MLN), lymph node yield (LNY) and ratio (LNR)) were significantly associated with all site and nodal recurrence in the univariate analysis (all P<0.05). Multivariate analyses revealed largest dimension>3cm, gENE and LNR>0.21 were associated with elevated both all site (HR [95%CI], 2.58 [1.67-4.00], 1.87[1.26-3.01], 1.68[1.11-2.42], all P<0.01) and nodal recurrences (HR[95%CI], 2.63[1.67-4.13], 1.90[1.15-3.12], 1.76[1.17-2.66], all P<0.01). LNR and gENE had interactive effect (all site recurrence: P for interaction = 0.009; nodal recurrence: P for interaction = 0.02). LNR was significantly associated with recurrence in patients without gENE (HR[95% CI], all site recurrence: 2.41[1.50-3.87]; nodal recurrence: 2.51[1.52-4.14], all P< 0.001), while when gENE appeared, LNR was no longer associated with recurrence (HR [95% CI], all site recurrence: 0.81[0.43-1.54], P=0.53; nodal recurrence: 0.85[0.43-1.67], P=0.64).Nodal factors have synergy effect in predicting recurrence in cN1b PTC patients. Increasing lymph nodes harvest may only decrease recurrence in patients without gENE, while not in gENE patients.© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.