Learn about the policies designed to fill the gaps in Medicare coverage -- called medigap insurance.

Even for those who have Medicare coverage, a serious illness or injury can cause financial havoc because of the bills Medicare does not cover. Responding to this risk, about two-thirds of all Medicare recipients aged 65 or over buy some kind of private health coverage -- called medigap insurance.

The term medigap comes from the notion that these insurance policies will cover the gaps in Medicare payments. Unfortunately, most medigap coverage is not nearly as complete as its advertising would lead you to believe.

Before you buy a medigap insurance policy, consider not only the services covered, but the amount of benefits and the monthly cost of the policy. Also pay attention to two other factors: how much premiums may rise in the years to come and, assuming you are willing to pay those premiums, whether you will be allowed to keep the policy.