Part A doesn't cover care from doctors who treat patients in the hospital. Those doctor bills -- such as from a surgeon, radiologist, oncologist, or primary care physician -- are covered instead by Medicare Part B. Nor does Part A cover emergency room care; that, too, is covered under Part B.

If travelling abroad, be aware that Part A covers care only in hospitals in the United States, including Puerto Rico, the U.S. Virgin Islands, Guam, and American Samoa. Even emergency hospital care while traveling outside the country isn't covered.

There are some hospital inpatient costs Part A doesn't cover. Private-duty nurses or a private room aren't covered unless they're ordered by a doctor who deems them medically necessary. And personal convenience items, such as television and telephone, aren't covered if the hospital bills them separately.

Finally, it's important to recognize that Part A pays only for medically necessary care, and only if it must be delivered on an inpatient basis. In other words, if you could receive the same treatment in a doctor's office or an outpatient clinic, Part A might not pay for it in the hospital. Likewise, there's no coverage for elective surgery. Also, even if Part A covers a hospital stay, it might stop coverage if you remain there after the hospital is ready to discharge you -- if, for example, because no one has arranged care for you at home.