OBJECTIVE:There has been an exponentially increasing interest in intraabdominal hypertension (IAH) and the abdominal compartment syndrome (ACS) over the last decade, and different definitions have been suggested. Nevertheless, there has been an impetus from experts in the field to modify these definitions to reflect our current understanding of the pathophysiology of these syndromes. An international multidisciplinary group of interested doctors met with the goal of agreeing on a set of definitions that could be applied to patients with IAH and ACS. The goal of this consensus group was to provide a conceptual and practical framework to further define ACS, a progressive injurious process that falls under the generalized term 'IAH' and that includes IAH-associated organ dysfunction. DESIGN:In total, 21 North American, Australasian and European surgical, trauma and critical care specialists agreed to standardize the current definitions for IAH, ACS and related conditions in preparation for the second World Congress on Abdominal Compartment Syndrome (WCACS). The WCACS-meeting was endorsed by the European Society of Intensive Care Medicine (ESICM) and the World Society on Abdominal Compartment Syndrome (WSACS). METHODS:The consensus conference (Noosa, Australia; December 7, 2004) was attended by 21 specialists from Europe, Australasia and North America and approximately 70 other congress participants. In advance of the conference, a blueprint for the various definitions was suggested. After the conference the participants corresponded electronically with feedback. A writing committee was formed at the conference and developed the final manuscript based on executive summary documents generated by each participant. The final report of the 2004 International ACS Consensus Definitions Conference has recently been published. This article will describe the long road towards this final publication with the evolution of the different definitions and recommendations from the initial suggestions in 2004 to the further refinement and final publications in 2006 and 2007. It will try to explain how we got there and will also give the percentage of agreement with each proposed definition by the participants. RESULTS:New definitions were offered for some terms, while others were discarded and not kept in the final manuscript. Different cut-offs for defining IAH and ACS were given, as well as broad definitions of primary, secondary and recurrent IAH/ACS. A classification system was introduced taking into account the duration, origin, and etiology of IAH. The use of an organ severity scoring method, by means of the Sequential Organ Failure Assessment (SOFA) score when dealing with ACS patients was not recommended as an adjunctive tool to assess morbidity in the final publication. CONCLUSION:This document reflects a process whereby a group of experts and opinion leaders suggested definitions for IAH and ACS. This document should be used as a reference for the next consensus definitions conference in March 2007.