Bone marrow transplantation using unrelated donors has become a clinical reality but a large number of challenges remain. One of the most important and a crucial one is locating a suitable donor. To cope with this very large registries have been formed but each of these lacks donors with phenotypes which occur in other registries. To facilitate the search process a collation system designated Bone Marrow Donors Worldwide (BMDW) was started. Several times a year it collects the phenotypes of all donors from all participating registries on a worldwide basis. The data are sorted by phenotype number of the broad antigens; the splits are specified immediately after the broad phenotypes. Here the experience with the first 11 editions is summarized. Although there is a steady increase in the numbers of donors and phenotypes included in BMDW, < 1% of the theoretically possible HLA-A, -B, -DR split phenotypes are so far represented. Furthermore, 70% of these phenotypes are unique, i.e. they occur in one donor only. As a result 30% of the donors have a phenotype which occurs in one registry only. Of 49 Europdonor donors who donated bone marrow, 8 (16%) had a phenotype which did not occur in any of the other registries. Because BMDW indicates in which registry a potential donor can be located, it can reduce search time by 75%. We conclude that the use of BMDW is the fastest and most cost-effective way to locate donors with rare phenotypes, whether or not they are of Caucasoid origin.