Inclusion Criteria:

- Diagnosis of JIA (any subtype).

- Age < 18 years at the time of enrollment.

- Receiving Abatacept at the time of enrollment as per treating physician's decision.

- Parent or legally acceptable representative willing to participate in the study and
sign the informed consent.

Exclusion Criteria:

- Pregnant or nursing female at the time of enrollment.

- Prior malignancies if the patient has not been malignancy free for at least 5 years.

- 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.

- Known poor compliance with clinic visits (based on physician judgment).