Paroxysmal nocturnal hemoglobinuria (PNH) is a rare and serious blood disorder that affects the red blood cells. It is characterized by the destruction of red blood cells and the release of hemoglobin into the urine and bloodstream, leading to anemia and other complications. Synonyms for PNH include Marchiafava-Micheli syndrome, Marchiafava-Micheli hemolytic anemia, and Marchiafava-Micheli disease. Other terms used to describe PNH include nocturnal hemoglobinuria and intravascular hemolysis. While PNH is a complex and difficult condition, it is important to seek medical attention promptly if experiencing symptoms such as weakness, fatigue, or dark urine, as early treatment can improve outcomes.