Porphyric Hemophilia is the disease that turns you into a vampire (see vampirism). There are three ways to acquire this disease. The first is fighting with a vampire and contracting it as you would any other disease. The second way is through the Dark Brotherhood faction. After reaching a certain rank you will be offered the chance to become a vampire by Vicente Valtieri, but if you decline you can always ask again later; although, if you continue to complete the Dark Brotherhood questline, you will lose this option as you will have to kill Vicente Valtieri. The third is by eating the beating heart during Mehrunes Razor add on.

The disease can bring you many combat-related benefits, as well as a few curses, as described in detail in the vampirism article.

For more information on being a vampire, see vampirism.