If you are traveling from another country to the United States, you may need travel insurance or medical travel insurance.

The U.K. Foreign & Commonwealth Office states the following on its website:  "Many people deeply regret not taking out travel insurance. They think their credit card accident cover, home insurance, or private health cover is sufficient."  They state that if you need to be returned to the U.K. via air ambulance it could cost thousands of pounds, and they add a following point, "Remember: the British Embassy or High Commission will not pay for this."

But fortunately, medical travel insurance is inexpensive, making it an easy option.