Interstitial lung disease occurs in approximately one-third of patients with polymyositis and dermatomyositis (PM/DM) and has an adverse effect on survival. It is commonly a component of early PM/DM and can precede the onset of muscle or skin disease. Its most common histopathology is nonspecific interstitial pneumonia. This is a more benign pattern, with respect to response to immunosuppression and also long-term survival, than the pattern of usual interstitial pneumonia seen in idiopathic pulmonary fibrosis. The clinical course of PM/DM lung disease is heterogeneous. Progressive and nonprogressive disease needs to be distinguished by clinical and physiologic monitoring to avoid over-treatment. Patients with ongoing functional deterioration mostly benefit from immunosuppression. The experience with corticosteroid monotherapy is discouraging but cyclophosphamide, given as daily oral or intravenous pulse therapy together with corticosteroids, was found to be beneficial in many patients. Other immunosuppressants may be of benefit as well, but the weight of the current evidence supports the use of cyclophosphamide first.