The following disease entities are being included into the idiopathic inflammatory myopathy group (IIM): dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM). These are primary inflammatory muscle diseases with substantial muscle weakening in their course. Everyone of the entities belonging to IIM is possessed of a particular clinical picture, as well as of histological and immunological features. In this paper, there have been briefly described classification, clinical pictures, supplementary diagnostic tests, treatment and up-to date views on IIM etiopathogenesis.