Preheat oven to 350 F. Lightly grease a 9x13 inch baking dish.
In a large soup pot, boil sweet potatoes whole until soft. Remove skins, and dice into bite-sized pieces.
Mix sweet potatoes, crushed pineapple, light brown sugar, and butter in prepared baking dish.
Bake for 45 minutes, or until casserole is mushy with no excess water in the dish.