The objective of this study was to assess the prevalence, clinical, histological and immunological characteristics, and the long-term outcome of polymyositis- (PM) and dermatomyositis- (DM) associated lung disease, and to define subgroups of lung-associated inflammatory myopathies. This retrospective study included 81 consecutive patients diagnosed with PM/DM. Pulmonary involvement was systematically investigated in relation to clinical symptoms by chest radiography, high resolution computed tomography and pulmonary function testing. Anti-synthetase autoantibodies (ASA) were analysed by ELISA and confirmed by protein and RNA immunoprecipitation methods. Statistical analyses were done with the Student t-test and Fisher exact test. Cumulative survival probabilities were estimated by the Kaplan-Meier method and Cox regression analysis. Fifty patients (61%) presented pulmonary involvement. Thirty-two (39%) had interstitial lung disease and five of them had devastating acute interstitial pneumonia with pneumomediastinum and an unfavorable prognosis. Histology showed diffuse alveolar damage in this subgroup and ASA were negative. Eighteen patients (22%) presented restrictive myopathic lung disease; in three of them respiratory muscles could not maintain ventilation. ASA were positive in 17 of the 50 patients (34%) and were significantly associated with interstitial lung disease (OR: 4.5 [95% CI: 1.3-15.3]), arthritis (OR: 6.0 [95% CI: 1.3-29.2]) and 'mechanic hands' (OR: 8.5 [95% CI: 1.7-41.4]); the presence of these autoantibodies did not imply worse survival prognosis. We concluded that clinical and immunological characteristics allowed the grouping of patients into different types of PM/DM lung-associated disease. Presence of ASA did not affect survival. ASA-negative patients with acute interstitial pneumonitis and pneumomediastinum had an unfavorable prognosis.