The Bubonic Plague wiped out over one third of the population of Europe.

33%

"The Black Death, or the Black Plague, was one of the deadliest pandemics in human history, widely thought to have been caused by a bacterium named Yersinia pestis (Bubonic plague), but recently attributed by some to other diseases. The pandemic is thought to have begun in Central Asia or India, and spread to Europe during the 1340s. The total number of deaths worldwide is estimated at 75 million people, approximately 25–50 million of which occurred in Europe. The Black Death is estimated to have killed 30% to 60% of Europe's population. It may have reduced the world's population from an estimated 450 million to between 350 and 375 million in 1400." "Figures for the death toll vary widely by area and from source to source as new research and discoveries come to light. It killed an estimated 75–200 million people in the 14th century. According to medieval historian Philip Daileader in 2007: The trend of recent research is pointing to a figure more like 45% to 50% of the European population dying during a four-year period. There is a fair amount of geographic variation. In Mediterranean Europe and Italy, the South of France and Spain, where plague ran for about four years consecutively, it was probably closer to 80% to 75% of the population. In Germany and England . . . it was probably closer to 20%." Source and further information: http://en.wikipedia.org/wiki/Black_death