Perfluoroalkyl acids (PFAAs) are a class of persistent, bioaccumulative and potentially toxic contaminants which have been found to be ubiquitously present in human serum samples. Determining the major human exposure pathway/s of perfluoroalkyl acids (PFAAs) is a crucial step in risk assessment and a prerequisite for the development of effective management strategies of these chemicals. Previous studies have suggested that diet, drinking water, indoor air and house dust are important exposure media. However, a mechanistic understanding of exposure to PFAAs has been hampered by the fragmented nature of exposure studies. The aim of this research project is to simultaneously quantify the internal and external exposure to PFAAs for a well-defined human cohort. By combining state of the art analytical techniques and exposure modeling tools human serum concentrations of PFAAs can be described as a mass balance of the intake and elimination and the dominant exposure pathways can be determined. This will be the first time that multiple exposure pathways of PFAAs are quantified for a single cohort and a major step forward in exposure assessment science.