The idiopathic inflammatory myopathies (IIM) of childhood are rare, multisystem autoimmune disorders, of which the most common is juvenile dermatomyositis (JDM). The criteria currently used to diagnose the paediatric IIMs, including both JDM and other childhood autoimmune conditions in which myositis may be a prominent feature, are somewhat outdated in relation to paediatric practice. Controversies surrounding the criteria for diagnosis have resulted in an international effort to define both the diagnostic and classification criteria in light of modern investigation and practice. Clinical features of these IIMs include muscle weakness and skin rash; however, these may be absent at disease onset. JDM patients require careful assessment of multiple organ systems, which can divided into musculoskeletal and extra-musculoskeletal, and examination should include validated disease measurement tools such as the Childhood Myositis Assessment Scale. Investigations include blood tests to assess generalised markers of inflammation as well as more specific markers of muscle inflammation; organ-specific investigations, such as MRI, and muscle biopsy are also often used. Treatment and management protocols include corticosteroids, methotrexate and other disease-modifying agents such as ciclosporin (cyclosporin) and intravenous immunoglobulin, as well as newer treatments such as tumour necrosis factor blockade or B-cell depletion. Management of children with JDM requires a multidisciplinary approach, including specialist physiotherapy, occupational therapy and nursing input. Two major international projects, the International Myositis and Clinical Studies Group (IMACS) and Paediatric Rheumatology International Trials Organisation (PRINTO) aim to standardise the assessment of these patients and measurement of their disease. The efforts of these large collaborative groups should provide much needed networks for mulitcentre trials in the future.