the objective was to evaluate the prevalence of patients at a high risk of having oSA by using a screening questionnaire and to investigate whether the questionnaire can predict patients who are at risk of cardiopulmonary events occurring during a bronchoscopy under sedation. We prospectively enrolled consecutive adult patients who underwent flexible bronchoscopies under moderate sedation. The snoring, tiredness, observed apnea, high blood pressure-body mass index, age, neck circumference and gender (Stop-Bang) questionnaire was used to identify patients at a high (score ≥ 3 of 8) or low risk (score < 3 of 8) of having OSA. The cardiopulmonary events included hypoxemia and hypotension. Multivariable logistic regression was performed with variables selected by the least absolute shrinkage and selection operator. The prevalence of a STOP-Bang score of ≥ 3 was 67.2% (195/290), and 36.9% (107/290) experienced cardiopulmonary events. The multivariable analysis adjusting for chronic obstructive pulmonary disease, chronic kidney disease, baseline Spo 2 , and procedure time revealed that a STOP-Bang score of ≥ 3 was significantly associated with cardiopulmonary events in a subgroup of patients without a history of cerebrovascular disease (adjusted odds ratio, 1.94; 95% confidence interval, 1.06-3.54). The STOP-Bang questionnaire can predict cardiopulmonary events occurring during this procedure. Trial registration: NCT03325153. Obstructive sleep apnea (OSA) is characterized by repetitive episodes of complete or partial upper airway obstruction occurring during sleep 1. It is suggested that about 1 billion adults worldwide may be affected by OSA 2. The prevalence of OSA-defined as more than five apneas or hypopneas per hour of sleep plus excessive daytime sleepiness-was 12.5% in men and 5.9% in women in the middle to old age general population 3,4. Overnight polysomnography is the gold standard for the diagnosis of OSA. However, it is time-consuming, labor-intensive, and costly 5,6. Although patients with OSA are at an increased risk of developing perioperative cardiac and pulmonary complications 7-10 , approximately 60% of those with moderate to severe OSA are not recognized preoperatively 11,12. Patients with OSA may experience obstructive episodes during procedures while under moderate sedation 13. However, the rate of adverse events in undiagnosed OSA patients undergoing bronchoscopies under moderate sedation remains poorly described. In early 2000, Sharma et al. reported that OSA was detected in threequarters of 23 patients without a previous diagnosis of sleep apnea while undergoing outpatient bronchoscopy or colonoscopy 14. Recently, a study with obese patients having bronchoscopy under moderate sedation showed that the incidences of procedural complications were similar between obese and non-obese patients. However, a subset (7%) of patients with previous polysomnography-proven OSA were more likely to have earlier termination