Background: The respiratory function is affected by obesity due to an increased deposition of fat on the chest wall. The objective of this study was to investigate the strength of the inspiratory respiratory muscles of obese individuals and the possible influence of bariatric surgery on it by measuring the maximum inspiratory pressure (MIP). Methods: Patients referred to a bariatric centre between the 3rd of October 2011 and the 3rd of May 2012 were screened preoperatively by a multidisciplinary team. Their MIP was measured at screening and 3, 6 and 9 months postoperative. In case of a preoperative MIP lower than 70% of predicted pressure training was provided supervised by a physiotherapist. Results: The mean age of 124 included patients was 42.9 +/- 11.0 years and mean BMI was 43.1 +/- 5.2 kg/m(2). The mean predicted MIP preoperatively was 127 +/- 31 in cm H2O and the mean measured MIP was 102 +/- 24 in cm H2O. Three patients (2.4%) received training. Three months after surgery the MIP was 76 +/- 26 cm H2O, after 6 months 82 +/- 28 cm H2O and after 9 months 86 +/- 28 cm H2O. All postoperative measurements were significant lower than preoperatively (P <0.05). The only influencing factor for the preoperative MIP was age (p = 0.014). Conclusion: The preoperative MIP values were significantly lower than the predicted MIP values, probably due to altered respiratory mechanics.