technically you should change both. if you havent scorched the rotors by going too long without changing the pads, then you should be fine. also if there is a lip around the outer edge on the surface of the rotor, then you should just get new rotors. i went with autozone cheapys about a year ago, cuz i needed rotors but wasnt ready to upgrade to the larger rotors like i am about to. if your runnin your brakes hard, i would go with aftermarket, but if your tryin to cut corners with the limited lifetime autozone speacial, just go get some $15 pads and call it a day.