Aims: There are limited data on the risk for sedation-related cardiopulmonary events in patients with undiagnosed obstructive sleep apnea (OSA) undergoing bronchoscopy. The aim of the study was to evaluate the prevalence of high-risk patients for OSA by a screening questionnaire, and to determine whether the questionnaire could predict patients who were at risk for cardiopulmonary events during bronchoscopy with conscious sedation. Methods: We prospectively enrolled consecutive patients who underwent bronchoscopy with conscious sedation from December 2016. The STOP-BANG questionnaire (SB) was used to identify patients at high risk for OSA (score, ≥ 3 of 8; SB+) or low risk (score ＜ 3 of 8; SB-). Cardiopulmonary events included hypoxemia and hypotension (a systolic blood pressure of ＜ 90 mm Hg or a decrease of more than 25% from the baseline). Airway maneuvers were defined as a chin lift, bag-mask ventilation, or unplanned endotracheal intubation. Results: Preliminary analysis was performed. Of 188 participants enrolled until August 2017, 180 were eligible for the analysis. The prevalence of SB+ was 66%. Cardiopulmonary events tended to be higher among patients with SB+ than SB- (45.4% vs 31.2%, P = 0.066). The rates of airway maneuvers were similar between SB+ and SB- patients (9.2% vs 11.5%, P = 0.637). In multivariable analysis, adjusted OR of SB+ was 1.85 (95% CI, 0.94-3.63; P = 0.074). Conclusions: A significant number of patients undergoing bronchoscopy with sedation were at risk for OSA. Cardiopulmonary events may occur at an increased frequency in these patients