Of the idiopathic interstitial pneumonias, idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP) have provoked the most debate and discussion. Although the two diseases are distinct entities, diagnosis is not always straightforward and requires a multidisciplinary approach, integrating clinical, radiological and histologic information. Although there is currently no effective treatment for either disease, the importance of differentiating NSIP from IPF lies in the management of the individual patient, with particular focus on outcome and pace of change, and enrollment into novel treatment trials of IPF.