Dermatomyositis is a rare inflammatory myopathy with characteristic skin manifestations and muscular weakness. The disease can be categorized as adult idiopathic, juvenile, or amyopathic dermatomyositis as well as that associated with a connective tissue disease or a malignancy. Immunologic factors are most likely involved in the pathogenesis of the disease; however, genetic and environmental issues may also play important roles. Treatment with immunosuppressive agents has proved successful in the majority of patients, although significant morbidity still occurs. (J Am Acad Dermatol 1998;39:899-920.) Learning Objective: At the conclusion of this learning activity, participants should be familiar with the clinical characteristics of adult idiopathic, juvenile, and amyopathic dermatomyositis as well as the histopathologic and immunopathologic characteristics of the disease.