This Phase III clinical study will assess the efficacy of BMN 270 defined as FVIII activity, during weeks 49-52 following intravenous infusion of BMN 270 and assess the impact of BMN 270 on usage of exogenous FVIII replacement therapy and the number of bleeding episodes from week 5 to week 52.

Inclusion Criteria:

1. Males ≥ 18 years of age with hemophilia A and residual FVIII levels ≤ 1 IU/dL as evidenced by medical history.
2. Must have been on prophylactic FVIII replacement therapy for at least 12 months prior to study entry.
3. Treated/exposed to FVIII concentrates or cryoprecipitate for a minimum of 150 exposure days.
4. No previous documented history of a detectable FVIII inhibitor of less than 0.6 Bethesda Units (BU).

Exclusion Criteria:

1. Detectable pre-existing antibodies to the AAV5 capsid.
2. Any evidence of active infection or any immunosuppressive disorder, including HIV infection.
3. Significant liver dysfunction, prior liver biopsy showing significant fibrosis, liver cirrhosis of any etiology or history of hepatic malignancy.
4. Evidence of any bleeding disorder not related to hemophilia A.
5. Active Hepatitis C.
6. Prior treatment with any vector/gene transfer agent.

Biological males only

First 52 weeks post infusion