Allogeneic hematopoietic stem cell transplantation (HSCT) represents the first choice of treatment or an important therapeutic option for numerous diseases. Several stem cell sources, such as bone marrow, mobilized peripheral blood stem cells, and umbilical cord blood, are suitable for HSCT in clinical practice. However, this procedure is strongly related to availability of a histocompatible donor. In order to increase the probability of finding a histocompatible donor, national and international registries have been developed. Voluntary donation of bone marrow or peripheral blood stem cells for HSCT, both in the related or unrelated setting, is a well-established procedure with an invaluable ethical significance. Even if both procedures are safe, they are not risk free; therefore, the greatest attention has to be paid to the donor and to the donation process through a careful monitoring protocol for donor safety.