Background: Abdominal compartment syndrome (ACS) is associated with high morbidity and mortality rates. Therefore, the need for a good diagnostic tool to predict intra-abdominal hypertension (IAH) and progression to ACS is paramount. Bladder pressure (BP) has been used for several years for intra-abdominal pressure (IAP) measurement but has the disadvantage that it is not a continuous measurement. In this study, a single-lumen central venous catheter (CVC) is placed through the abdominal wall into the abdominal cavity to continuously and directly monitor the intra-abdominal pressure (CDIAP). The aim of this study was to evaluate the use of CDIAP to measure BP as a representative of the true IAP. Methods: Both BP and CDIAP were prospectively recorded on a variety of surgical patients admitted to the intensive care unit (ICU) from March 2003 up to December 2004. At the end of the surgical procedure, the CVC was placed through the abdominal wall and connected to a pressure transducer. In addition, the BP was measured through the urine drainage port after clamping the catheter and filling the bladder with So ml of 0.9% saline. At least three paired measurements (BP and CDIAP) were performed for at least one day on the ICU in a standardized manner at preset time intervals on each patient. The paired measurements were compared using the Bland-Altman (B-A) method. Data are presented as mean standard deviation. Results: Over a period Of 22 months (March 2003 until December 2004), 125 paired measurements of both BP and CDIAP were recorded on 25 patients. The mean age was 72.4 +/- 6.6 years. Eighteen patients underwent central vascular surgery, and seven patients with peritonitis received laparotomy. The mean CDIAP was 11.4 +/- 4.8 (range 2-30) mmHg, and the BP was 12.9 +/- 5.3 (range 3-37) mmHg. The mean difference between CDIAP and BP was 1.6 +/- 2.7 mmHg. There was an acceptable level of agreement (intraclass correlation 0.82) between IAP measured by BID and IAP measured via CDIAP. Conclusion: Continuous direct intra-abdominal pressure measurement proved that the BP measurement approach of Kron is representative of the IAP. CDIAP measurement is accurate and makes it easier for the nursing staff to be informed of the IAP.