The idiopathic inflammatory myopathies are a heterogeneous group of disorders affecting both adults and children. Clinical features can include muscle weakness, skin disease and internal organ involvement. A large number of autoantibodies, directed against cytoplasmic or nuclear components, can now be identified in these patients and specific clinic-serological syndromes have been described. Laboratory testing to identify many of these autoantibodies is becoming easier, and here we discuss the clinical utility of autoantibodies in myositis both in terms of facilitating diagnosis, predicting disease course and informing management decisions.