Inclusion body myositis (IBM) is an inflammatory myopathy with distinctive clinicopathologic features. The etiology of IBM remains elusive. The immune-mediated basis for this disease has been challenged by evidence implicating a number of divergent etiologic factors. These factors include mitochondrial deletions, nitric oxide induced oxidative stress, myonuclear breakdown, and abnormal accumulation within muscle fibers of brain-specific Alzheimer type proteins. The treatment of IBM with conventional immunosuppressive agents has been disappointing. Therapeutic approaches currently under study or consideration are beta-interferon and synthetic anabolic hormones.