Background: Flexible bronchoscopy (FB) is a procedure accepted to be safe in general, with low complication rates reported. On the other hand, it is known that patients with pre-existing respiratory failure have developed hypoventilation following FB. In this study the effects of FB on respiratory muscle strength were investigated by measuring maximum respiratory pressures. Methods: One hundred and forty patients, aged between 25 and 90 years, who had undergone diagnostic bronchoscopy between February 2012 and May 2012, were recruited to the study. Pre- and post-procedure maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were measured. A correlation between the MIP and MEP changes and patient characteristics and FB variables were investigated. Results: Significant decreases in both MIP and MEP values were observed following FB (p < 0.001 for both). Decreases were attributed to the midazolam used for sedation. Significant decreases in respiratory muscle strengths were observed especially in the high-dose midazolam group, compared to both low-dose and non-midazolam groups. Conclusions: It was determined that respiratory muscle weakness may arise post-procedure in patients who have undergone FB, and this is constitutively related to midazolam premedication. Respiratory muscle weakness might play a role in potential hypoventilation in critical patients who undergo FB. © 2012 Tulek et al.: licensee BioMed Central Ltd.