Systemic juvenile idiopathic arthritis (JIA) is a type of JIA in which a child experiences a very high fever and in some cases a rash, on a daily basis. Joint pain or swelling may appear a few weeks or months after the fevers begin.

Systemic juvenile idiopathic arthritis is the least common yet potentially most serious type of JIA. Organs such as the heart, lungs, liver, spleen, or lymph nodes may eventually be affected. Episodes of whole-body (systemic) symptoms can last for weeks to years and can come and go during the first years of the disease. While some children have one course of this disease that lasts 2 to 4 years, others continue to have mild joint pain and flares of other symptoms. A few have ongoing destructive arthritis, often into adulthood, even with treatment.

Systemic juvenile idiopathic arthritis is sometimes also called Still's disease.