Nanoparticles made of amphiphilic block copolymers comprising biodegradable core-forming blocks are very attractive for the preparation of drug-delivery systems with sustained release. Their therapeutic applications are, however, hindered by low values of the drug-loading content (DLC). The compatibility between the drug and the core forming block of the copolymer is considered the most important factor affecting the DLC value. However, the molecular picture of the hydrophobic drug copolymer interaction is still not fully recognized. Herein, we examined this complex issue using a range of experimental techniques in combination with atomistic molecular dynamics simulations. We performed an analysis of the interaction between itraconazole, a model hydrophobic drug, and a poly(ethylene glycol) poly(lactide-co-glycolide) (PEG-PLGA) copolymer, a biodegradable copolymer commonly used for the preparation of drug delivery systems. Our results clearly show that the limited capacity of the PEG-PLGA nanoparticles for the accumulation of hydrophobic drugs is due to the fact that the drug molecules are located only at the water polymer interface, whereas the interior of the PLGA core remains empty. These findings can be useful in the rational design and development of amphiphilic copolymer-based drug-delivery systems.