I've long known about Hepatitises A, B and C—unrelated viral infections that all share the same name because they all cause inflammation of the liver. Until just a couple of minutes ago, however, I had no idea that there was also a Hepatitis D—which you only seem to be able to get if you already have Hep B—and a Hepatitis E. There's also a hypothetical, but never proven, Hepatitis F and a former Hepatitis G—the name of which was changed to GB virus C after researchers realized that, while it infected humans, it didn't actually appear to do any damage. No inflamed livers, no entry into the Hepatitis club. (Via Tia Ghose)