In critically ill patients an intra-abdominal hypertension (IAH) is a frequent phenomenon. An IAH is defined as an intra-abdominal pressure (IAP) persistently ≥ 12 mm Hg and an abdominal compartment syndrome is defined as an IAP with a persistent pressure ≥ 20 mm Hg in combination with newly occurring organ failure. The bladder pressure serves as a surrogate parameter for the IAP, which should be measured noninvasively in a standardized manner. An undetected and untreated IAH worsens the prognosis of critically ill patients.