Polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) are three major catogories of idiopathic inflammatory myopathies. These disorders are clinically, histologically, and pathogenically distinct. Imumunopathogenically is PM T-cell-mediated disorder directed against muscle fibers. PM generally presents in patients over the age of 20 years and is more prevalent in females. Patients present with neck flexor weakness and symmetrical proximal arm and leg weakness, which develops over several weeks or months. Bohan´s and Peter´s clinical, biochemical, EMG and histopathological criteria are practical and sensitive for diagnosis of PM. The course of PM is mostly chronic and may require long-term therapy. PM is usually responsive to corticosteroids (prednisone is the treatment of choice in PM) and to immunosuppressive agents (azathioprine, cyclophosphamide, etc). In cases of PM refractory to corticosteroids and immunosuppressive agents has IVIg a beneficial response.