This article describes the basic definitions, indications and complications of hematopoietic stem cell transplantation. The different modes of transplantation (autologous, allogeneic-related and allogeneic-unrelated transplantation) are explained with regard to the underlying immunological processes and consequences for duration of treatment, distribution of age, complications, lethality, and for the family of the patient. In our department, the duration of the hospital stay was (median) 44 days for autologous BMT, 45 days for allogeneic-related BMT and 66 days for allogeneic-unrelated BMT. Six to twelve years old children showed a peak for allogeneic related transplantations; these children were treated mainly for relapse of acute lymphoblastic or myeloid leukemias. Patients over 15 years old showed a peak for autologous transplantations; due to the research focus of our center, Ewing's sarcoma was the main underlying disease in this age group. Allogeneic-unrelated transplantations were uniformly distributed over the whole age range from nine months to 24 years.