BACKGROUND: Xenotransplantation carries inherent risks of infectious disease transmission to the recipient and even to society at large, and it should only be carried out with strict regulation and oversight. In collaboration with the International Xenotransplantation Association, the University Hospital Geneva, and the World Health Organization, an international inventory has been established (www.humanxenotransplant.org) aiming to collect basic data on all types of currently ongoing or recently performed xenotransplantation procedures in humans. METHODS: We collected information from publications in scientific journals, presentations at international congresses, the internet, and declarations of International Xenotransplantation Association members on xenotransplantation procedures in humans performed during the past 15 years. RESULTS: We identified a total of 29 human applications of xenotransplantation, including 7 that were currently ongoing. Procedures involved transplantation of xenogeneic cells, i.e., islets of Langerhans, kidney cells, chromaffin cells, embryonic stem cells, fetal and adult cells from various organs or extracorporeal perfusion using hepatocytes, liver, spleen, or kidney. The treatments were performed in 12 different countries, 9 of them having no national regulation on xenotransplantation. CONCLUSION: Several clinical applications of cell xenotransplantation are ongoing around the world, often without any clear governmental regulation. This information should be used to inform national health authorities, healthcare staff, and the public, with the objective of encouraging good practices, with internationally harmonized guidelines and regulation of xenotransplantation.