Non-specific interstitial pneumonia/fibrosis (NSIP) is a relatively new entity among idiopathic interstitial pneumonias. This disease is pathologically characterized by varying proportions of interstitial inflammation and fibrosis that appear to occur over a single, short period of time, and is clinically characterized by a generally good prognosis. Although corticosteroid therapy is widely considered to be effective for treatment of this disease, we report a case of Group II NSIP which developed during treatment with corticosteroid 4 months after acute respiratory distress syndrome (ARDS). This case suggests that any group of NSIP may be developed after ARDS, and that low-dose corticosteroid treatment is not sufficient to prevent the development of NSIP.