Juvenile idiopathic arthritis is inflammatory arthritis that begins in childhood, specifically before 16 years of age. It is not one disease but a group of related conditions defined by pediatric classification. The main patterns are: oligoarticular, which involves four or fewer joints early on; polyarticular, which involves five or more joints and is further divided by rheumatoid factor status into RF-positive and RF-negative forms; and systemic onset, also called Still’s disease, characterized by daily fevers, rash, and often systemic features in addition to arthritis. A common thread across these subtypes is persistent synovitis, meaning ongoing inflammation of the joint lining, which in turn can interfere with growth. Chronic joint inflammation near growth plates can lead to growth-related problems such as limb-length discrepancies or angular deformities if not well controlled. This pediatric-onset pattern and the distinct subtypes reflect how JIA is categorized, distinguishing it from adult-onset rheumatoid arthritis or osteoarthritis, which occur later in life and have different patterns (often older age at onset, more erosive disease, and usually different joint involvement).