An estimated 300,000 to 500,000 cases of type 1 diabetes exist today in the United States. Despite strict monitoring and attempts at control, people with type 1 diabetes still face the prospect of diminished health and earlier death than the general population. Islet transplantation offers an alternative to insulin usage and a potential treatment for type 1 diabetes mellitus. There are more than 30 islet transplant centers in the world focusing their efforts on the challenges and methods of this procedure. As the field of islet transplantation matures and the number of islet transplants performed increases, detailed analyses on factors that predict patient and graft survival are needed. This increased amount of data will allow for a better understanding of the safety and efficacy of islet transplantation. In response to the need for more complete information in the field, the National Institute of Diabetes and Digestive and Kidney Diseases is sponsoring the North American Collaborative Islet Transplant Registry (CITR). The mission of CITR is to expedite progress and promote safety in islet/beta-cell transplantation through the collection, analysis, and communication of comprehensive and current data on all islet/beta-cell transplants performed in North America. Compiling and analyzing data from all transplant centers in North America will accelerate the identification of both critical risk factors and key determinants of success, and thereby guide transplant centers in developing and refining islet/beta-cell transplant protocols, leading to an advancement in the field of islet transplantation. Participation in CITR is voluntary, and more than 22 transplant centers have been invited to join. Seven centers are actively participating in CITR, with an additional 11 centers in the process of joining. Both an executive committee and a scientific advisory committee guide CITR. All islet transplants performed in North America since January 1, 1996, are captured by the CITR database. Through an electronic, Internet-based data capture system, quality control procedures, and minimization of duplicate efforts at the transplant center, the most relevant and succinct information are entered. From these data a comprehensive report will be published annually. In addition, special analyses will be performed and published periodically.