More than 1,1 million donors are registered in the DKMS Deutsche Knochenmarkspenderdatei donor center. Since the start of the program, 5,930 have donated bone marrow or peripheral blood stem cells. These donors were included in a follow up program with questionnaires and blood cell counts 1, 6, and 12 months, and thereafter annually. Non responding donors were interviewed via a telephone call which enables us to have a follow-up of all donors. The age range at harvest was 18 to 60 years (median 32.4 years). The cumulative observation years were 13,350 years for 2,644 bone marrow donors and 7,980 years for 3,286 peripheral blood stem cell donors. No severe immediate complications occurred during the harvests. Seven out of 2,644 bone marrow donors (0.3%) suffered from long lasting severe local pain. Three of them were hospitalized within 6 weeks after donation with hematoma, local infection or severe local pain. One donor of the peripheral blood stem cell group suffered from severe hyperthyroidism 14 days after donation. In this donor, euthyroidism was documented at the day of leukapheresis. Antibodies to thyroid peroxidase were already detectable in retrospectively analyzed cryopreserved samples from these time points. TSH receptor stimulating immunoglobulin appeared only after harvest accompanied by symptoms of hyperthyroidism. Rheumatoid arthritis was diagnosed in 2 peripheral blood stem cell donors (interval from harvest: 0 days and 1 year) and joint complaints were addressed by additional 4 donors. Vascular events were seen in 4 peripheral blood stem cell donors (cerebral ischemia in 3 donors 3 months, 1 year and 2.5 years after donation; myocardial infarction in a 58 years old male donor 2 years after donation) and in one bone marrow donor (Brown-Séquard-syndrome 4 years after harvest). Four donors of the bone marrow group and 5 donors of the peripheral blood stem cell group developed malignancies during the follow-up observation. Four donors of the bone marrow group died 1 year to 8 years after donation (sudden death, car accident, suicide, and unknown). In unrelated donors, bone marrow harvests and peripheral blood stem cell donations are safe procedures in specialized collection centers. Even in a large donor center as DKMS, the numbers of adverse events in the follow up period are small. The documentation of diseases early after harvest (autoimmune diseases, thromboembolic events etc.) needs a careful follow-up. A case-controlled study with sex-, age- and HLA-matched volunteers within the donor pool will therefore be initiated by DKMS.