Objective To investigate the prevalence of obstructive sleep apnea hypopnea syndrome ( OSAHS) in patients with idiopathic pulmonary fibrosis ( IPF) and its clinical significance. Methods Sleep quality and breathing disorders were measured by polysomnography and the relationship with lung function was analyzed in 20 IPF patients. Results Thirteen of 20 subjects ( 65% ) had OSAHS as defined by an AHI ≥5 events per hour. Three subjects ( 15% ) had mild OSAHS ( AHI,5 to 20 events per hour) , and 10 subjects ( 50% ) had moderate-to-severe OSAHS ( AHI≥20 events per hour) . The sleep architecture in these patients showed a reduction in sleep efficiency, rapid eye movement ( REM) sleep and slow wave sleep, and a marked sleep fragmentation due to an increased arousal index. The AHI was negatively correlated with FVC% pred ( r =-0.672, P=0.001) and FEV1% pred ( r =-0.659, P=0.002) , and positively correlated with body mass index ( BMI) ( r=0.791, Plt;0.0001) . Conclusions OSAHS is a common comorbidity in IPF. Early treatment of OSAHS may improve quality of life and the prognosis of patients with IPF.