The original Joint Outcome Study (JOS) enrolled 65 boys with hemophilia from 16 sites nationally. The subjects were randomized to one of two arms (prophylaxis or an enhanced episode-based treatment)and were followed prospectively until the age of six. At the age of six, the proportion of children on each treatment arm who developed bone or cartilage damage as determined by X-Ray or MRI was assessed. In addition, the function and structure of the index joints (defined as knees, ankles, and elbows)were evaluated using a physical assessment scale specially designed for preschool children.

The specific aim of the Joint Outcome Study Continuation (JOSC) is to extend observations of the children participating in the original JOS until the subjects reach the age of 18 years in order to determine the natural history of joint development in hemophilia and the impact of primary or secondary prophylaxis on the prevention, limitation, or reversal of hemophilic arthropathy. In addition, plasma and DNA will be collected and banked yearly for current and future studies of biomarkers and predictors of hemophilia outcomes.

Inclusion Criteria:

• Enrolled in the original JOS study, "A Randomized Prospective Study for the Prevention of Joint Disease in Children with Factor VIII Deficiency"
• Written, informed consent of parent or guardian for the proposed study
• The local hemophilia treatment center staff must evaluate the family's participation in the original treatment protocol and determine that the family is capable of complying with the continuation protocol

Exclusion Criteria:

• Unable or unwilling to record the study information

Study population will be invited based on their enrollment in the original Joint Outcome Study (JOS). This population