Aplastic anemia is defined as peripheral blood pancytopenia associated with unexplained hypocellularity of the bone marrow without excess of blast cells. Untreated patients die from bleeding or infections as a consequence of marrow failure. During the last 20 years, prognosis of aplastic anemia has greatly improved. Probability of survival is 92% at three years after HLA-identical sibling bone marrow transplantation, and 87% at five years after intensive immunosuppressive treatment. The aim of treatment of aplastic anemia is to improve peripheral blood counts in order that the patients become independent from transfusions and free from risks of opportunistic infections.