Remove mushroom stems; chop and set aside. Reserve mushroom caps.
Brown sausage in a skillet, stirring to crumble; drain. Combine sausage, mushroom stems, breadcrumbs, salt, and pepper; mix well. Spoon into mushroom caps.
Place stuffed mushrooms in a lightly greased 13- x 9- x 2-inch baking dish. Broil 6 inches from heat 5 minutes or just until breadcrumbs are lightly browned.