US is a powerful tool for the assessment of joint synovitis in children with JIA and has been shown to be more accurate than clinical examination in detecting synovial disease. Recent studies have documented the presence of US-detected synovial pathology in children with JIA in clinical remission. US assessment enables the differentiation of joint synovitis from tenosynovitis, may help detect enthesitis and is valuable for capturing cartilage damage and early bone erosions. Guidance to local injection therapy represents an important application of US in routine care. Although US has a great potential for diffusion among paediatric rheumatologists, several issues need to be addressed. In particular, a thorough knowledge of US anatomy of joints in growing children is necessary to interpret US findings in JIA patients. The present review examines the potential role of US in the assessment of joint disease in children with JIA.