Polymyositis and dermatomyositis are uncommon autoimmune inflammatory disorders of muscle, which have been grouped under the term idiopathic inflammatory myositis. Current therapy does not take into account the different pathophysiologic mechanisms of these entities and the firstline option consists of corticosteroids. These entities have been extensively studied but almost none of the treatments, even those generally accepted as efficacious, have been established through controlled clinical trials. Furthermore, there are no validated response criteria for myositis, although recent studies have started to define outcome measures for application in future therapeutic trials. Controversy also surrounds the definition of patients with treatment– resistant myositis. Refractory myositis could be defined as intolerance or inadequate response to corticosteroids with or without an adequate regime of at least one other immunosuppressive agent. It is difficult to advance the treatment of uncommon severe illnesses through controlled trials of new regimens.