Interstitial lung disease (ILD) associated with amyopathic dermatomyositis (ADM) is a rare and sometimes fatal condition whose clinical features are not well understood. The goal of this study was to clarify the characteristics of ILD based on its development. Eighteen patients diagnosed with ILD associated with ADM were assigned to 1 of 2 groups: (1) a rapidly progressing group, which included patients who developed abnormal lung findings within 1 month of being diagnosed with ADM (n=9); or (2) a slowly progressing group, which including patients who developed lung findings greater than 1 month after diagnosis of ADM (n=9). Serum creatine phosphokinase and C-reactive protein levels were higher in the rapidly progressing group than in the slowly progressing group. Further, arterial pH was higher and PaO(2)/F(I)O(2) was lower in the rapidly progressing group than in the slowly progressing group. On thoracic high-resolution CT, traction bronchiectasis was present in 4 of the 9 rapidly progressing patients but not in any patients of the slowly progressing group. All 9 slowly progressing patients survived with proper treatment, but only 4 of the 9 rapidly progressing patients survived. In ADM, appropriate investigations are likely required for the early diagnosis of ILD. Our data suggest that ILD associated with ADM can be classified into 2 clinical subtypes based on the time course of pulmonary involvement. Patients with rapid progression in respiratory symptoms should undergo intensive treatment as soon as possible to promote favorable outcomes.