Snapper head, good question. I've never seen a foreign 1st class medical in the USA but I doubt it. Your question should probably be posed to the FAA. I'm sure that with a quick search, you could find their website and ask the question. One bit of advice though, if you have to get an FAA medical, find out who the local pros give all of their repeat business to and that should be your Dr. I've had friends and relatives who've had no previous problem with approval, change doctors because they were out of town or just relocated to a new domicile, lose their medical through the very subjective process. Once you get disapproved, it's an uphill battle from there. Good luck.