Use of vedolizumab in pediatric inflammatory bowel disease (IBD) often requires an interval intensification from standard dosing due to distinct pharmacokinetics (PK) in children. Adult population PK models found inclusion of albumin, weight, anti-TNF naivety and antibodies-to-vedolizumab (ATV) as covariates of drug clearance (CL) improved model accuracy. We aimed to build a population-PK model for children and identify novel covariates of drug CL to better account for pediatric-specific variability in vedolizumab PK.