Some costs that Medicare doesn't cover, including coinsurance, copayments and deductibles, health emergencies in foreign countries, at-home recovery, and preventive care.

Medicare includes Part A, which covers medically necessary treatments in a hospital, and Part B, which covers medically necessary doctors' services and outpatient care as well as Part A deductibles. The Medicare Health Plans, parts C through L, include these basic benefits and addtional coverage. Plans are standardized so buyers can compare provider offerings. Part J offers the most benefits; parts K and L were new in 2005. Insurers are not required to offer all Medicare Supplement, also known as Medigap, plans. Each spouse must buy coverage separately. New in 2006 are Medicare prescription drug plans, which offer alternatives to the original Medicare plan. People in many areas may choose Medicare Advantage Plans, which provide extra benefits and can free an enrollee from needing any Medigap plans. For more information about Medicare and Medigap, go to www.medicare.gov.

Most people eligible for Medicare.

People with private or other health plans that cover expenses Medigap plans insure. Massachusetts, Minnesota and Wisconsin offer their own Medigap policies. The affluent may choose to self-insure. People with Medicare Advantage Plans or those on Medicaid may not be eligible for Medigap policies.

During your six-month Medigap open enrollment period, which begins the first day of the month in which you are 65 years old and enrolled in Medicare Part B. If you are losing health coverage from another source because you are eligible for Medicare, you can apply for a Medigap policy before your open enrollment period starts in order to assure continuous coverage.

Monthly premiums.