Based on the current multidisciplinary classification of idiopathic interstitial pneumonia (IIP) organized by ATS/ERS, nonspecific interstitial pneumonia (NSIP) is considered as one type of IIP. An incidence of idiopathic NSIP is relatively small and possesses clinical features that are different than idiopathic pulmonary fibrosis (IPF) and usual interstitial pneumonia (UIP). Because there is little evidence of a long-term prognosis in patients with NSIP, some of them have an unfavorable prognosis similar to IPF/UIP. We review the significance of prognostic factors that have been reported in patients with IPF/UIP by applying them to patients with NSIP. The association with collagen vascular diseases focuses on etiologic background. Finally, the article discusses whether NSIP could be an early lesion of UIP based on the reported evidence and our own professional experiences.