Aplastic anemia - bone marrow failure (AA) is defined as pancytopenia with hypocellular bone marrow without signs of marrow fibrosis or of presence of abnormal cells. Recent studies showed that most of AA cases might be mediated by immune mechanisms. Toxic agent leads to expression of neoantigens or cryptic antigens on the surface of pluripotent hematopoietic stem cells with subsequent activation of immune effector cells and induction of stem cell apoptosis. Histopathological findings obtained from bone marrow biopsy are crucial for diagnosis of AA. Hypoplastic MDS, PNH, hairy cell leukemia and late manifestation of congenital cytopenias must be excluded in differential diagnosis. Allogeneic stem cell transplantation from HLA matched related donor or combined immune suppression represent the first line treatment for patients with severe AA (SAA). Transplantation from unrelated donor may be a second line treatment for patients who failed to respond to immunosuppressive therapy. Recent studies showed eltrombopag or its combination with immune supression as an effective therapeutic approach to AA patients. Up to 15 % of AA patients may later develop PNH, MDS or acute leukemia. An influence of disturbed immune mechanisms as well as of immunosuppressive treatment on the development of clonal proliferation is currently discussed. Key words: aplastic anemia - diagnosis - eltrombopag - immunosuppression - transplantation - treatment.