The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) established the Collaborative Islet Transplant Registry (CITR) in September 2001. In its inaugural year, CITR represents the efforts of 12 collaborating North American islet transplant centers reporting 86 islet transplant recipients' data (1999-2003) and 173 processed pancreata leading to 158 infusion procedures. Recipient median age was 42.2 years, duration of diabetes was 30 years, and over 66% of the recipients were female. Twenty-eight patients received a total of 1 islet infusion, 44 patients received 2 islet infusions, and 14 patients received 3 islet infusions. The median age of the deceased donor was 44 years and body mass index was 28.2. Median time from cross clamp to pancreas recovery was 27 minutes, while duration of cold ischemia was 7 hours. Over 77% of the processing facilities used a density gradient for islet purification. For recipients of only 1 infusion, approximately 8665 total islet equivalents/kg were infused; recipients of 2 infusions received 14,102 islet equivalents/kg, and recipients of 3 infusions received 22,922 islet equivalents/kg. At 6 months after the last infusion, 61.1% of the recipients were reported to be insulin independent; at 12 months, 57.9% were reported to be insulin independent. There have been no deaths reported to CITR; 45 serious adverse events were reported. Through its collaboration with the islet transplant community and its interaction with professional societies and federal agencies, CITR is positioned to provide current and comprehensive information on clinically significant outcome measures in islet transplantation.