Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by the classic clinical triad of corpuscular hemolytic anemia, thrombophilia and cytopenia. This is caused by an acquired mutation of the PIG(phosphatidylinositol glycan)-A gene of the pluripotent hematopoetic stem cell. This results in a deficiency of GPI(glycosylphosphatidylinositol)-anchors and GPI-anchored proteins on the surface of affected blood cells. Flow cytometry is the standard for diagnosis and measurement of type and size of the PNH clone. Treatment of PNH is mainly symptomatic. Allogeneic bone marrow transplantation is the only curative option in case of severe complications during the course of the diseases. A new targeted treatment strategy is the inhibition of the terminal complement cascade with a monoclonal antibody (eculizumab). As shown in clinical studies this is efficient to reduce complement mediated intravascular hemolysis, reduce the need for transfusions, improve the quality of life in patients with PNH and reduce the risk for thromboembolic complications, which are the main cause of mortality in PNH.