The pressure within the abdominal cavity is normally little more than atmospheric pressure. However, even small increases in intra-abdominal pressure can have adverse effects on renal function, cardiac output, hepatic blood flow, respiratory mechanics, splanchnic perfusion and intracranial pressure. Although intra-abdominal pressure can be measured directly, this is invasive and bedside measurement of intra-abdominal pressure is usually achieved via the urinary bladder. This cheap, easy approach has been shown to produce results that correlate closely with directly measured abdominal pressures. Significant increases in intra-abdominal pressure are seen in a wide variety of conditions commonly encountered in the intensive care unit, such as ruptured aortic aneurysm, abdominal trauma and acute pancreatitis. Abdominal compartment syndrome describes the combination of increased intra-abdominal pressure and end-organ dysfunction. This syndrome has a high mortality, most deaths resulting from sepsis and multi-organ failure. Detection of abdominal compartment syndrome requires close surveillance of intra-abdominal pressure in patients thought to be at risk of developing intra-abdominal hypertension. The only available treatment for established abdominal compartment syndrome is decompressive laparotomy. Prevention of abdominal compartment syndrome after laparotomy by adoption of an open abdomen approach may be preferable in the patient at significant risk of developing intra-abdominal hypertension, but this has not been demonstrated in any large trials. Most surgeons prefer to adopt a ‘wait and see’ policy, only intervening when clinical deterioration is associated with a significant increase in intra-abdominal pressure.