Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia with highly variable clinical symptoms making the diagnosis and prediction of its outcome difficult. It is caused by the expansion of a hematopoietic progenitor cell that has acquired a mutation in the X-linked phosphatidylinositol glycan class A (PIGA) gene that results in deficiency of the glycosylphosphatidylinositol anchor structure responsible for fixing a wide spectrum of proteins particularly CD55 and CD59. The clinical features of this disease arise as a result of complement-mediated hemolysis in unprotected red cells, leukocytes, and platelets as well as the release of free hemoglobin. Patients may present with a variety of clinical manifestations, such as anemia, thrombosis, kidney disease, smooth muscle dystonias, abdominal pain, dyspnea, and extreme fatigue. PNH is an outstanding example of how an increased understanding of pathophysiology may directly improve clinical symptoms and treat disease-associated complications when we inhibit the terminal complement cascade. This topic will discuss PNH overview to assist specialists looking after PNH patients.