['The incidence of obstructive sleep apnea (OSA) in interstitial lung disease (ILD) has been reported at different frequencies in several studies. The aims of our study were to evaluate the frequency of OSA in ILD and to analyze the relationship between polysomnography (PSG) findings and pulmonary function, disease severity, parenchymal involvement, and Epworth Sleepiness Scale (ESS) scores.', 'ILD patients with parenchymal involvement were evaluated. The disease severity was assessed using an index consisting of body mass index (BMI), carbon monoxide diffusion capacity, the Modified Medical Research Council dyspnea scale, and the 6-min walking distance. All of the patients had lung function, chest X-ray, PSG, ESS scoring, and an upper airway examination. Patients with a BMI\u2009≥\u200930 or significant upper airway pathologies were excluded.', 'Of 62 patients, 50 patients comprised the study group (14 male, 36 female; mean age 54\u2009±\u200912.35\xa0years, mean BMI 25.9\u2009±\u20093.44\xa0kg/m(2)) with diagnoses of idiopathic pulmonary fibrosis (IPF; n\u2009=\u200917), stage II-III sarcoidosis (n\u2009=\u200915), or scleroderma (n\u2009=\u200918). The frequency of OSA was 68\xa0%. The mean apnea-hypopnea index (AHI) was 11.4\u2009±\u200912.5. OSA was more common in IPF patients (p\u2009=\u20090.009). The frequency of rapid eye movement-related sleep apnea was 52.9\xa0%. The frequency of OSA was higher in patients with a disease severity index ≥3 (p\u2009=\u20090.04). The oxygen desaturation index and the AHI were higher in patients with diffuse radiological involvement (p\u2009=\u20090.007 and p\u2009=\u20090.043, respectively).'] Is obstructive sleep apnea common in patients with interstitial lung disease?