A: 

You need some statement, either break or goto.

DavGarcia
+3  A: 

Every case needs to have either a break; or goto case statement in C#

Agent_9191
or return, or throw
Charles Bretana
+1  A: 

It requires the break or you'll get a compiler error. You can have multiple cases with one block of code but control cannot fall through to the next case.

Andrew Kennan
+1  A: 

You use a break in C#, just like in C++. However, if you omit the break you must replace it with another other control transfer (e.g. goto case 1;).

See http://msdn.microsoft.com/en-us/library/06tc147t(VS.71).aspx

Artelius