Imaging assessments of the joints of children with juvenile idiopathic arthritis (JIA) are challenging, owing to the unique features of the growing skeleton. Traditionally, imaging studies in childhood arthritis have been based on conventional radiography. However, in the past few years, interest in the use of MRI and ultrasonography has increased. As a result, imaging has become a main area of clinical and research investigation in paediatric rheumatology. The chief advance in the field of conventional radiography has been the development and validation of paediatric scoring systems for the assessment of radiographic progression. Several studies have shown that MRI provides a precise quantification of synovitis in children with JIA. Furthermore, a high frequency of bone marrow oedema and bone erosions has been found early in the disease course. Ultrasonography has been proven to be superior to clinical examination in detecting synovitis, tenosynovitis and enthesitis. A high frequency of subclinical synovitis has been demonstrated in patients with JIA who have clinically inactive disease using both MRI and ultrasonography. However, more information from healthy children is needed to enable differentiation of the bone and cartilage abnormalities that reflect damage from those that are part of normal development using MRI or ultrasonography. This Review provides a summary of the current information on conventional radiography, ultrasonography and MRI in JIA and highlights the advantages and limitations of each imaging modality.