Background: Idiopathic pulmonary fibrosis (IPF) is a progressive disease with a 3-year median survival. Lung volume and diffusion capacity at rest are usually used to monitor the clinical course. Because of high mortality, identification of patients at high risk is crucial for treatment strategies such as lung transplantation (LTX). This study was designed to determine if tumor markers could accurately characterize disease severity and survival in patients with IPF. Methods: The study population consisted of 61 patients with progressive IPF referred for LTX. Pulmonary function tests, cardiopulmonary exercise test, 6-min walk distance test, and Doppler echocardiogram were assessed at baseline and compared with tumor marker levels. Participants were prospectively followed for at least 25 months to determine the relationship between test parameters and survival. Tumor marker levels were reassessed in patients who underwent LTX. Forty-one age- and sex-matched patients (21 LTX recipients) with COPD served as control subjects. Results: In the IPF group, nine patients (14.7%) died during follow-up and 20 (32.8%) underwent LTX. Univariate analysis showed correlations between carbohydrate antigen (CA) 125 and FEV 1%(P = .0001). CA 19-9 yielded the best correlations with exercise parameters and PAP. Significant correlation with survival was noted with CA 15-3(P = .04) only. All tumor marker levels decreased significantly following LTX, except CA 125. CA 15-3 had the largest decrease(P = .001). Among the COPD group, tumor marker levels before LTX were significantly lower compared with the IPF and did not decrease following LTX. No patient in either group developed malignancy. Conclusions: CA 15-3 levels may predict disease severity in IPF. Levels decreased in patients with IPF but not with COPD following LTX and were not associated with malignancy. This preliminary observation suggests that mucin has a role in the pathogenesis of IPF and possibly is a marker for disease activity. © 2012 American College of Chest Physicians.