If you are eligible for Medicare but haven't signed up for Part B, the 2010 General Enrollment Period ends March 31. Those who don't sign up before the deadline will have to wait until the next enrollment period begins in January 2011.
Because enrollees pay a monthly premium for Part B, some with employer health insurance don't sign up. Those older than 65 who lose their health insurance because they leave their jobs have an eight-month Special Enrollment Period to sign up for Part B that begins after they stop working. But if you elected to receive continuing group health coverage under COBRA, be aware your Special Enrollment Period also begins when you lose your job, not when you exhaust COBRA benefits.
All Americans are automatically enrolled in Medicare Part A, which covers hospital costs, when they turn 65. Part B, which is voluntary, pays for doctors' visits and some supplies.
For more information, download "Understanding Medicare Enrollment Periods" at medicare.gov/ Publications/Pubs/pdf/11219.pdf.