Relatively few studies address the treatment of specific histopathological subgroups of idiopathic interstitial pneumonia (Table 2). The best data on corticosteroid responsiveness in UIP and desquamative interstitial pneumonia were published in 1978 by Carrington et al.21 They retrospectively reviewed patients with UIP and desquamative interstitial pneumonia and found that when treated with corticosteroids, 11% and 62%, respectively, improved as measured by a combination of clinical, physiological, and radiographic indices. The same patients, when untreated during a different period, had 0% and 22% improvement, respectively.21 The criteria used for histopathological classification at that time did not distinguish UIP from NSIP, likely augmenting the response rate for UIP. More recent studies have found similarly poor response rates to corticosteroids for patients with UIP (8%-17%).9,22,23 No prospective treatment studies exist for NSIP or RBILD. However, retrospective reviews of observational studies in which most patients received corticosteroids have suggested excellent responsiveness for these diseases.9,12,14,23 Respiratory bronchiolitis–associated interstitial lung disease appears to resolve in most patients with smoking cessation alone.13,14 No good data exist on corticosteroid therapy for acute interstitial pneumonia, with one study of 29 patients showing no significant difference in survival with or without treatment.24 Taken together, these studies demonstrate a distinct difference in corticosteroid responsiveness on the basis of histopathological subgroup.