However, Original Medicare and Medicare private health plans must cover your medical care you get outside of the U.S. in the following limited cases:
Medicare will pay for emergency services in Canada if you are traveling a direct route, without unreasonable delay, between Alaska and another state and the closest hospital that can treat you is in Canada.
Medicare will pay for medical care you get on a cruise ship if:
The ship is registered to the U.S.;
The doctor is registered with the Coast Guard; and
You get the care while the ship is in U.S. territorial waters. This means the ship is in a U.S. port or within six hours of arrival at or departure from a U.S. port.
Medicare may pay for non-emergency in-patient services in a foreign hospital (and connected physician and ambulance costs). It is covered if it is closer to your residence than the nearest U.S. hospital that is available and equipped to treat you medical condition. This may happen if, for example, you live near the border of Mexico or Canada.
Some supplemental insurance, such as Medigap plans, provide coverage for foreign travel. Medigap plans C through G and M and N cover 80 percent of the cost of emergency care abroad during the first two months of a trip with a $250 deductible and up to $50,000 in a lifetime.
Some Medicare private health plans also cover emergency care when you travel outside the United States. Check with your plan to see what costs and rules apply when you travel outside of the United States.
http://www.medicareinteractive.org/page2.php?topic=counselor&page=script&slide_id=339
My Father still works, and has to travel to Europe alot on business, and because of this, keeps his employer's private health insurance.