Declining to Enroll in Medicare Part B
QUESTION: I am covered for health insurance on a group health plan. Do I have to enroll in Medicare Part B ?
ANSWER: No, but there could be some consequences to not enrolling, so do your homework!
Be sure you understand the benefits offered on your group plan. Make sure there are no gaps in your coverage.
The most critical concern comes should you ever leave or loose that group coverage. In most cases, once group coverage ends you will enter a special enrollment period that runs for eight months from the time your group coverage ends. Failing to enroll in Medicare Part B during the initial enrollment period or your special enrollment period may result in a penalty being added to your Medicare Part B monthly premium once you enroll.
SOURCE: http://www.socialsecurity.gov/ ; search for publication 10043.