An adequate drug dosage at treatment initiation is particularly relevant for critically ill patients. An inadequate dosage may result in therapeutic failure, potentially severe adverse events, and unnecessary health expenditures. At present, due to the higher incidence of childhood obesity, primary care physicians are more commonly faced with this population, so they need to make appropriate therapeutic decisions. Knowledge of the resulting pharmacokinetic alterations caused by increased body fat is critical. The optimal drug dosage is not completely defined and the correct body descriptor should be used, although there is no consensus on which is the most adequate one. The objective of this update is to gain insight on pharmacokinetic alterations that affect dosage in the critically ill obese pediatric patient and, specifically, those related to the drugs most commonly used in this population during their stay in the pediatric intensive care unit.