Names given by physicians to human ailments range from the esoteric to the simplistic, and they may provoke in the non-physicians anything from intimidation to incredulity, but probably very few are as picturesque as paroxysmal nocturnal hemoglobinuria. In addition, whereas medical terms do not always adhere to the meaning that words have in plain English (a “benign” tumor can kill if it is in the brain, while “pernicious” anemia can be quickly reversed by one shot of vitamin B12), the phrase paroxysmal nocturnal hemoglobinuria (PNH) describes very accurately the telltale sign of this condition. Indeed, the patient may be a child or an old-age pensioner, a male or a female, may be from any part of the world, and may have been always well, until she or he wakes up one morning to the rather unpleasant surprise that the urine has turned intensely dark, as though it contained blood. In fact, it contains hemoglobin released from massive destruction of red cells within the bloodstream, and hence filtered through the renal glomeruli. Thus, in the jargon of hematologists, PNH is classified as a hemolytic anemia in which hemolysis is intravascular (