The measurement of intra-abdominal pressure (IAP) is gaining importance in critical care units because of its prognostic value. The standard method of measurement is intravesical. When the IAP is high, the condition is referred to as intra-abdominal hypertension. The elevation may be compensated for if it is not excessive or if the increase was not rapid, or it might have various repercussions, in which case abdominal compartment syndrome (ACS) is diagnosed. The pathogenic mechanism that underlies ACS is the response of a territory predisposed to a process of ischemia and reperfusion, with release of inflammatory cytokines and formation of free radicals (anaerobic metabolism). Clinical manifestations comprise elevated IAP, oliguria, difficult mechanical ventilation with hypoxia and hypercapnia, and diminished cardiac output. ACS leads to multisystem dysfunction and, if not treated, to multiple organ failure and death. The rapid establishment of appropriate treatment measures is important. The first line of treatment is medical but definitive surgical treatment should not be delayed.