If you are covered under Medicare Part A, but originally opted not to apply for Medicare Part B, now's your opportunity to enroll in Part B. The general enrollment period runs from January 1 through March 31.

But first, you may be wondering: what are Parts A and B? And why would someone get one and not the other? Here are the nuts and bolts.

Medicare Part A (hospital insurance) helps pay for inpatient care in a hospital or skilled nursing facility following a hospital stay, some home health care, and hospice care.

Medicare Part B (medical insurance) helps pay for doctors' services and many other medical services and supplies not covered by hospital insurance.

When you first become eligible to apply for Medicare Part A, you also have the option of enrolling in Part B for a monthly premium. Some people decide not to because they do not want to pay the premium or for other reasons. But you may discover that as your medical needs change, it is to your advantage to enroll. That's where enrollment periods come into play.

When you first become eligible for Part A, you have a seven-month period (your initial enrollment period) in which to sign up for Part B. After the initial enrollment period, you can only sign up during a later year's general enrollment period.

Each year, the Medicare general enrollment period runs January 1 through March 31. Your coverage begins the following July. But keep in mind that, for most people, the monthly premium increases 10 percent for each 12-month period you were eligible for, but did not enroll in, Medicare Part B.

So if you are covered under Medicare Part A and you've been thinking about applying for Part B, now is the time to act. Learn more about Medicare by reading Social Security's publication on the subject at www.socialsecurity.gov/pubs/10043.html. You also can learn a lot about Medicare by visiting www.socialsecurity.gov and selecting "Medicare" at the top of the page on the right side.

Or visit Medicare's website at www.medicare.gov.

Ginny Jordan is a Public Affairs Specialist for the Social Security Administration. Her weekly column on all things Social Security appears in the Sunday Edition of the Sun-Sentinel.

Ginny has agreed to let us reprint her articles here for your convenience.

Thank you Ginny!