Purpose: Bilevel positive airway pressure (BPAP) devices do not only titrate BPAP pressures but also measure residual respiratory event. The aim of this study is to determine the accuracy of BPAP derived residual apnea-hypopnea index (AHI). Methods: We studied 100 patients who underwent in laboratory overnight PSG (polysomnography) using BPAP. Exclusion criterias are patients with central sleep apnea and complex central apnea syndrome. Age, sex, body mass index (BMI), neck circumference, Epworth Sleepiness Scale (ESS), and comorbidity were recorded at the time of diagnostic PSG for each patient. Residual AHI obtained from BPAP (BPAP-AHI) was compared simultaneously with AHI from an overnight PSG on BPAP (PSG-AHI) using Bland- Altman analysis and Wilxoson signed-rank test. Results: BPAP markedly supressed the respiratory event during the titration (PSG-AHI = 3,5 event per hour) On the other hand BPAP-AHI was 5,6 event per hour.) There was statistically significant difference between residual AHI obtained from BPAP and AHI from overnight PSG on BPAP (p Bland-Altman analysis showed that there is no agreement between BPAP-AHI and PSG-AHI (AHI mean difference of 3,60) and the limits of agreement for the AHI were from 2,40-4,79. Conclusion: The accuracy of measuring residual respiratory events for BPAP device has not been extensively evaluated and compared with the gold standard method, in-laboratory PSG-based measurements. In this study, BPAP was not able to identify residual respiratory events equivalent to the use of PSG.