Participants will be a representative (random) sample of individuals from the comprehensive hemophilia treatment centres at HCFMUSP and SickKids. Boys between the ages of 7 and 18 years (inclusive) will be identified from the clinic ledgers at each of the centres. Using a computer generated random number list, proportionately stratified for Hemophilia A and B, and for moderate and severe disease (based on the baseline clinic proportions)