Inclusion Criteria:

1. Diagnosis of JIA (any subtype)
2. Age < 18 years at the time of enrollment unless currently or previously enrolled in an abatacept clinical trial and received abatacept
3. Receiving Abatacept at the time of enrollment as per treating physician's decision or received abatacept in a clinical trial
4. Parent or legally acceptable representative willing to participate in the study and sign the informed consent

Exclusion Criteria:

1. Pregnant or nursing female at the time of enrollment
2. Prior malignancies if the patient has not been malignancy free for at least 5 years.
3. Any serious acute or chronic medical condition other than JIA, including chronic infection, which would compromise the patient's ability to participate in the study
4. Known poor compliance with clinic visits (based on physician judgment)