Outcome following cardiac arrest and cardiopulmonary resuscitation is dependent on critical interventions, particularly early defibrillation, effective chest compressions, and advanced life support. Utstein-style definitions and reporting templates have been used extensively in published studies of cardiac arrest, which has led to greater understanding of the elements of resuscitation practice and progress toward international consensus on science and resuscitation guidelines. Despite the development of Utstein templates to standardize research reports of cardiac arrest, international registries have yet to be developed. In April 2002 a task force of ILCOR met in Melbourne, Australia, to review worldwide experience with the Utstein definitions and reporting templates. The task force revised the core reporting template and definitions by consensus. Care was taken to build on previous definitions, changing data elements and operational definitions only on the basis of published data and experience derived from those registries that have used Utstein-style reporting. Attention was focused on decreasing the complexity of the existing templates and addressing logistical difficulties in collecting specific core and supplementary (i.e., essential and desirable) data elements recommended by previous Utstein consensus conference. Inconsistencies in terminology between in-hospital and out-of-hospital Utstein templates were also addressed. The task force produced a reporting tool for essential data that can be used for both quality improvement (registries) and research reports and that should be applicable to both adults and children. The revised and simplified template includes practical and succinct operational definitions. It is anticipated that the revised template will enable better and more accurate completion of all reports of cardiac arrest and resuscitation attempts. Problems with data definition, collection, linkage, confidentiality, management, and registry implementation are acknowledged and potential solutions offered. Uniform collection and tracking of registry data should enable better continuous quality improvement within every hospital, EMS system, and community.