Background: Recent data suggests that increased intra-abdominal pressure (IAP) is one factor associated with the morbidity of morbidly obese patients, who have a BMI >35 kg/m2. IAP has been proposed to be an abdominal compartment syndrome (ACS). This study investigated the characteristics of IAP in morbidly obese patients. Methods: 45 morbidly obese patients (mean BMI 55±2 kg/m2) had IAP measured using urinary bladder pressure. Results: The mean IAP for the morbidly obese group was 12±0.8 cmH2O, increased when compared to controls (IAP=0±2 cmH2O). The IAP correlated to the sagittal abdominal diameter, an index of the degree of central obesity (r=+0.83, P2O, while those without these morbidities had an IAP of 9±0.8 cmH2O. Conclusion: We conclude that IAP is increased in morbid obesity. This increased IAP is a function of central obesity and is associated with increased morbidity. The degree of IAP elevation correlates with increased co-morbidities. We also conclude that elevation in IAP in morbid obesity is not a true ACS but represents a direct mass effect of the visceral obesity.