The noninflammatory myopathies are a diverse group of diseases, some of which may mimic the autoimmune-mediated idiopathic inflammatory myopathies in their clinical presentation. They include certain metabolic, toxic, and infectious myopathies, as well as muscular dystrophies. In addition to muscle weakness, these forms of myopathy may present with exercise intolerance and muscle pain. Special testing techniques are often required to establish the diagnosis. This review focuses on those noninflammatory myopathies that should be included in the differential diagnosis of idiopathic inflammatory myopathy.