This is an investigator-initiated, industry-funded, multi-centre, international study that will be carried out prospectively at hemophilia treatment centres across Canada, the Czech Republic and Australia with SickKids as the coordinating site. The study will use a central laboratory not directly affiliated with any of the participating sites. Enrollment target is 50 participants, both adult and pediatric with severe hemophilia A receiving Advate, who will each complete a 2-point and 6-point pharmacokinetic (PK) sampling. The main aim is to compare the results of a 2 sample PK using clinically practical time points and myPKFiT™ (a web-based, population PK Bayesian tool) to a 6 sample population PK to determine whether the results obtained are in good agreement.