If you plan to travel at all in the U.S. sign up for part B. It will be cheaper than travel ins. in the U.S. If there is any chance at all, even a remote chance, that you may one day move back to the U.S., do not opt out of part B. Personal experience is my source of information. You will pay a penalty for the rest of your life. Your choice, but I would advise not opting out of part B.