Background: The fluid responsiveness of patients who are mechanically ventilated is evaluated using the reversible fluid loading technique known as passive leg raising. Objective: This study purpose to determine if intra-abdominal hypertension, which reduces venous return, affected the ability of passive leg raising to detect fluid responsiveness in critically ill patients. Patient and methods: Our study is a prospective study done at the critical care Medicine Department of Helwan University Faculty of Medicine on 400 mechanically ventilated patients with a pulse pressure variation greater than 12%. The esophageal Doppler was used to continually monitor the stroke volume. The bladder pressure was used to calculate intra-abdominal pressure. Fluid loading with 500 ml of saline was conducted after a passive leg-raising exercise and a return to baseline, with hemodynamic parameters recorded at each stage. Results: Four hundred patients were divided into two groups based on their response to passive leg raising: responders (at least a 12% increase in stroke volume) and non-responders (all patients in both groups were responders to volume loading). Two hundred patients responded to passive leg raising (50%), whereas the non-responders (i.e. false negatives) were similarly 50%. At baseline, the non-responders to passive leg raising had considerably greater median intra-abdominal pressure than the responders to passive leg raising (20 [5.5]- vs 10 [4.5], respectively, with a p-value < 0.001). Conclusion: Passive leg raising has false negatives are caused by intra-abdominal pressures more than 12 mmHg. In severely sick ventilated patients, intra-abdominal pressure (IAP) should be assessed before doing passive leg raising.