The purpose of this study is to evaluate bone mineral density in adult subjects with hemophilia versus a comparator population without hemophilia (non-hemophilia age- and gender-matched database) by using the following diagnostic means: dual-energy X-ray absorptiometry (DXA) scanning, clinical scales, quality of life (QOL) scales and biomarkers. In addition to this osteoporosis study, hemophilic arthropathy of the knee with respect to loss of knee cartilage will also be explored by using magnetic resonance imaging (MRI substudy). No investigational product will be dispensed.

Inclusion Criteria:

• Male and at least 25 years old at the time of screening
• Moderately severe or severe hemophilia A or B (factor VIII or factor IX <= 2% by chart documentation)
• Ambulatory (ie, not wheel chair dependent)
• Performance status - ECOG of 0 or 1 (= out of bed at least 75% of time)
• Willing and able to comply with the requirements of the protocol and is able to give informed consent

Additional inclusion criteria for MRI Substudy:

• Baseline knee joint space width is >= 3mm at the medial or lateral aspect of either knee as measured by weightbearing fixed flexion PA X-ray
• Able to undergo 1.5 or 3T MRI

Exclusion Criteria:

• Inability to position properly for DXA
• Presence of orthopedic hardware or other artifact in the lumbar spine (L1-L4) or either proximal femur
• Prior documentation of being HIV positive
• Radiosynovectomy or surgical synovectomy within the last 6 months
• Current or past treatment with bone active drugs
• Long-term corticosteroid use [defined as 7.5-mg prednisone daily (or equivalent) for >= 3 months]
• If subject is family member or employee of the investigator

Additional exclusion criteria for MRI Substudy:

• Any contraindication or relative contraindication to MRI
• Less than 3mm knee joint space width at the medial and lateral aspect of both knees on baseline X-ray evaluation
• Knee bleed within 30 days of informed consent
• Prior total knee arthroplasty (TKA)