How many episodes are there in high school of the Dead?

Answer 1

Its is expected to have 12 episodes, counting those 11 already aired.

Update:

There are serious rumors going around that a second season of the anime will be produced in the near future, and the estimated time of release is somewhere early next summer(2011). although only rumors, several interviews suggest they are correct, but that one of the production artists has changed. although its not a huge deal, dedicated fans might notice a slight difference in the animation.

Answer 2

12 episodes and 1 OVA. You really should be able to look these things up yourself though.