More than two thirds of the world's hemophiliacs currently face a drastically shortened life of pain and disability because they do not have access to safe factor concentrates, as these products are highly expensive and in limited supply. For these individuals, gene therapy remains an important avenue of hope because of its potential for a durable cure following a single therapeutic manipulation. The results of recent hemophilia gene clinical trials are encouraging, although they have failed to demonstrate sustained correction of the bleeding diathesis. Although many obstacles still remain, continuing technologic improvements have resulted in impressive advances in this field, which bodes well for patients with hemophilia and other genetic disorders.