Background: Pleuroparenchymal fibroelastosis (PPFE) is a rare interstitial pneumonia with upper lobe predominance and fibroelastosis. Although definite diagnosis requires surgical lung biopsy (SLB), SLB is often difficult because of its complications such as refractory pneumothorax. Objective: To evaluate urinary desmosines (degradation product of mature elastin) as a novel biomarker in patients with PPFE. Methods: Biopsy-proven patients with PPFE (n = 14) were prospectively enrolled. Levels of urinary desmosines in patients with PPFE were measured with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and compared with those in patients with idiopathic pulmonary fibrosis (IPF), patients with chronic obstructive pulmonary disease (COPD), and controls. Results: Levels of urinary desmosines were significantly higher in patients with PPFE than those in patients with IPF (48.4 vs. 28.6 ng/mg creatinine, p = 0.034), patients with COPD (8.0 ng/mg creatinine, p < 0.001), or controls (17.4 ng/mg creatinine, p < 0.001). Desmosines discriminated between PPFE and IPF (area under the curve [AUC] = 0.708), and between PPFE and controls (AUC = 0.956). However, levels of desmosines were not correlated with physiological parameters in patients with PPFE. Conclusions: Urinary desmosines may be a useful diagnostic biomarker in patients with PPFE. Measurement of desmosines combined with specific clinical and radiological features of PPFE may lead to an accurate diagnosis without SLB in patients with PPFE. (C) 2016 Elsevier Ltd. All rights reserved.