Prediction of the pharmacokinetics of orally administered drugs in children is of importance to optimize the efficacy and safety of pediatric medicines. Physiologically based pharmacokinetic (PBPK) models can be helpful for this purpose. However, application of these tools is limited by significant knowledge gaps regarding the physiological and anatomical changes which occur with age. This study aimed at investigating the age-dependent differences in oral absorption of a poorly soluble model compound, carbamazepine (CBZ) in children, infants, and neonates. We developed an oral absorption model in GastroPlus