Inasmuch as the clinical features of the idiopathic inflammatory myopathies are not easily differentiated from those of other similar rheumatic and neurologic conditions, diagnosis is often difficult. Various classification criteria for polymyositis and dermatomyositis have been suggested by a number of investigators. The most commonly accepted and used criteria include symmetric proximal muscle weakness, serum elevations of muscle enzymes, the classic electromyographic and muscle biopsy findings of inflammatory myopathy, and the typical skin rash of dermatomyositis. Although these criteria are clinically useful, they can result in misdiagnoses and inappropriate therapies. They also result in heterogeneous patient groups being selected for clinical and laboratory studies. Furthermore, they do not include recent findings related to the myositis-specific autoantibodies and magnetic resonance imaging of muscle that have been found to be important adjuncts in assessing patients with muscle weakness or elevations of muscle enzymes. A modification to the Bohan and Peter criteria is proposed to include myositis-specific autoantibodies and magnetic resonance imaging. This proposal could initiate productive discussions and investigations of the sensitivity and specificity of new classification criteria for myositis and could ultimately enhance our treatment capabilities.