Unrelated donor SCT activity is increasing, and in 5-10% of cases a subsequent donation of stem cells or donor lymphocytes may be requested. Second donations of stem cells are not associated with an increased chance of donor complications, but the yield of CD34+ cells may be lower in some donors. It is acceptable practice for any registry to request subsequent donations and it is recommended that donors should be counselled about this possibility before their first donation. Guidance is provided on the requirements for further medical assessment, the procedures used to agree requests, frequency and timing of donation and timing and duration of donor follow up.