Due to new, sensitive methodologies, the rate at which factor VIII gene mutations are found is increasing rapidly. The next five years should lead to the discovery of a wide range of defects as well as potential new hot-spots for mutations. Advances in understanding the protein will also provide new insights into the effects of particular mutations. Tremendous strides have been made in carrier detection and prenatal diagnosis. Already diagnosis is possible in 70% of cases with the factor VIII intragenic polymorphisms. Although there is still room for improvement in availability, speed, and cost of the test, many families in the United States and Europe are benefiting from this sensitive detection method.