We examined the effect of body mass index (BMI) on clinicopathological features of papillary thyroid carcinoma (PTC).The clinical data of 4476 patients with PTC who underwent surgical treatment were retrospectively analyzed. According to the different BMI of patients, it can be divided into underweight (BMI < 18.5kg/m2), normal weight (18.5 ≤ BMI < 24.0kg/m2), overweight (24 ≤ BMI < 28kg/m2) and obese (BMI ≥ 28kg/m2). Spearman correlation analysis was performed to assess the relationship between the BMI and the size of PTC tumor. Multivariate binary logistic regression analysis was performed to estimate the association of overweight and obesity with clinicopathological features of PTC.There was a positive correlation between the BMI and PTC tumor size (r=0.087, P<0.001). As compared with normal weight patients with PTC, overweight and obese patients with PTC had a greater risk of bilaterality (OR=1.295, OR=1.669), multifocality (OR=1.273, OR=1.617), ETE (OR=1.560, OR=2.477), T (3+4) stage (OR=1.482, OR=2.392) and recurrence risk (intermediate-high risk) (OR=1.215, OR=1.718) (P<0.05 for all). As compared with normal weight patients with PTMC, overweight and obese patients with PTMC had a greater risk of bilaterality (OR=1.341, OR=1.737), multifocality (OR=1.244, OR=1.640), ETE (OR=1.992, OR=2.080), T (3+4) stage (OR=1898, OR=2.039) and recurrence risk (intermediate-high risk) (OR=1.458, OR=1.536) (P<0.05 for all).Overweight and obesity were significantly associated with aggressive clinicopathological features of PTC and PTMC. The impact of overweight and obesity should be considered when choosing treatment decisions for PTC and PTMC.Copyright © 2022. Published by Elsevier Inc.