The prize is not awarded posthumously; however, if a person is awarded a prize and dies before receiving it, the prize may still be presented. Individuals who died in the months between their nomination and the decision of the prize committee were originally eligible to receive the prize. This has occurred twice: the 1931 Literature Prize awarded to Erik Axel Karlfeldt, and the 1961 Peace Prize awarded to UN Secretary General Dag Hammarskjöld. Since 1974, laureates must be thought alive at the time of the October announcement. There has been one laureate, William Vickrey, who in 1996 died after the prize (in Economics) was announced but before it could be presented. On October 3, 2011, the laureates for the Nobel Prize in Physiology or Medicine were announced; however, the committee was not aware that one of the laureates, Ralph M. Steinman, had died three days earlier. The committee was debating about Steinman's prize, since the rule is that the prize is not awarded posthumously. The committee later decided that as the decision to award Steinman the prize "was made in good faith", it would remain unchanged.

More Info: www.wikipedia.org