The hallmark of juvenile idiopathic arthritis is synovial inflammation, and the goal of treatment is to suppress inflammation to prevent cartilage damage and bone erosions. Ultrasound and MRI are widely used imaging modalities in evaluating disease burden and response to treatments and are superior to clinical examination alone. However, differentiating between the normal appearance of the developing skeleton and pathologic conditions can be difficult, particularly in early disease. Larger, long-term studies are needed to standardize imaging definitions and protocols and to fully understand the clinical implications of imaging findings.