Resistance to antiepileptic drugs (AED) remains a major problem in clinical epileptology. This pharmacoresistance is independent of the choice of AEDs. Different hypotheses have been proposed to explain the neurobiological basis for pharmacoresistance in epilepsy. The transporter hypothesis is the mostly investigated theory. Hereby, overexpression of multidrug efflux transporters, such as P-glycoprotein (Pgp), at the blood-brain-barrier (BBB) is thought to be involved in pharmacoresistance in epilepsy by extruding AEDs from their target site. Accumulating evidence supports an overexpression of Pgp in pharmacoresistant epilepsy. Molecular Imaging studies provide unique opportunities for the in-vivo study of the transporter hypothesis in the central nervous system (CNS). Several studies demonstrated that positron emission tomography (PET) with [11C]-radiolabled Pgp substrates is a promising tool for in vivo investigation of Pgp function at the rat, monkey and human BBB. Quantification of Pgp over activity in epilepsy patients by in vivo imaging could be highly useful because altered treatment strategies or novel AED could then be applied.