Walls and Ceilings - water damage to wall/ceiling

we have a split level home. Recently I decided to revamp our downstairs bathroom. As I removed the wall paper on one wall I saw that the wall underneath was damp, moldy and water damaged. The damage looked like it was there for a while. So, I started removing the drywall to see where the water was coming from. There is a chimney behind that wall. traced the problem up to the roof. Found the leak and fixed it. However, the water ran down the chimney, through the house and finally ended up dripping into that area of the bathroom. The damage included a very small portion of the ceiling. My question is, how much of the damaged ceiling should I remove? The damaged area is approx. 6"x6"square and in an inside corner.

Stacey, fixing drywall is easy. If it is a small area remove it all.
You must remove any damp drywall.
I like to replace stud to stud or joist to joist.
I would also take a bleach solution as spray effected areas. Always watch for wires, etc.