A 61-year-old man received an aorto-iliac reconstruction after he was admitted because of a ruptured abdominal aortic aneurysm. Postoperatively, he developed cardiopulmonary insufficiency with anuria. After the intra-abdominal pressure had risen to 40 cmH2O (measured by a urinary bladder catheter), it was decided to perform a relaparotomy. Immediately after abdominal decompression--without correction of any other intra-abdominal pathology--the diuresis increased and several other cardiopulmonary parameters improved significantly. When a critically ill patient shows a rapid increase of the intra-abdominal pressure above a critical level an acute abdominal compartment syndrome may develop. This syndrome consists mainly of potentially fatal cardiopulmonary and renal insufficiency, for which (re)laparotomy with abdominal decompression is the only correct treatment.