Pirfenidone has been studied and authorized in Idiopathic Pulmonary Fibrosis (IPF), but not in other, progressive forms of fibrotic interstitial lung disease (prog fILD). RELIEF was a double-blinded, placebo controlled, prospective phase II trial of pirfenidone (2403 mg/d) in patients with prog fILD (annual decline in % pred. FVC ≥ 5 %) despite conventional treatment (EudraCT 2014-000861-32). 127 Patients with collagen-vascular disease-ILD (n=37), fibrotic non-specific interstitial pneumonia (n=27), chronic hypersensitivity pneumonitis (n=57), and asbestos-related lung fibrosis (n=6) were included until the study was stopped due to futility (analysis initiated due to low recruitment). The primary endpoint was absolute change in % pred. FVC from baseline until week 48 and was analysed using rank ANCOVA (analysis of covariance). Changes in 6MWD, DLco and TLC were analysed by Wilcoxon rank sum test. Imputation for missing data including deaths was done in the final, but not the futility interim analysis. Pirfenidone was generally well tolerated. Antecedent FVC decline was confirmed. 5 deaths occurred in placebo, 1 in verum arm. We observed a lower decline in % pred. FVC as well as in 6MWD in the verum arm reaching significance when applying pre-specified imputation, but not without. Decline in DLco was significantly lower in the verum arm regardless of imputation. Sensitivity analyses without imputations and slope analysis with mixed effects models did not reach significance. Although limited by the low number of patients, the results of our study suggest that pirfenidone, added to conventional therapy, reduces disease progression in patients with progressive fILD.