Most patients with interstitial lung disease (ILD) associated with collagen vascular diseases (CVD) have a chronic indolent course with a relatively favorable prognosis; however, acute progression has been reported in some polymyositis-dermatomyositis patients. This study evaluated the prevalence, clinical features, and outcome relative to the presentation type of ILD in polymyositis-dermatomyositis (PM-DM). Ninety-nine patients with newly diagnosed polymyositis-dermatomyositis seen at the Asan Medical Center in Korea between January 1990 and December 2004 were enrolled. The clinical, radiological, and pathological findings were retrospectively reviewed. ILD were divided into acute (dyspnea within 1 month before diagnosis) or chronic types. ILD was found on chest radiographs in 33 patients (33.3%), and 11 (33.3%) of these were considered acute. The acute group presented with more severe respiratory symptoms, hypoxemia, and poorer lung function. Patients with an acute presentation had ground glass opacity and consolidation on high-resolution computed tomography (HRCT), in contrast to reticulation and honeycombing in the chronic type. Surgical lung biopsy of one acute-type patient revealed diffuse alveolar damage, whereas biopsies in the chronic type showed usual interstitial pneumonia (UIP) in four cases and nonspecific interstitial pneumonia (NSIP) in another four. Eight acute-type patients (72.7%) died of respiratory failure within 1-2 months despite steroid therapy. The 3-year mortality rate of the chronic-type patients (21.2%) was not statistically significantly different from that of the patients without ILD (10.2%). In polymyositis-dermatomyositis, the acute, severe form of ILD was not infrequent.