Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a large casserole dish.
Bring a large pot of lightly salted water to a boil. Stir in shell pasta and cook 12 minutes, or until tender but still firm. Drain, and transfer to a large bowl.
Mix cream of mushroom soup, Cheddar cheese, and pimentos with the pasta. Pour into the prepared casserole dish. Top with crushed crackers.
Cover dish, and bake 30 minutes in the preheated oven. Remove cover, and continue baking 15 minutes, until cheese is bubbly and crackers are lightly browned.
