The Medicare supplement plan type with the biggest market share continues to gain share.
The number of Medicare enrollees who signed up for Medigap Plan F coverage increased to 4.6 million in December 2011, up 9.6% from the total in December 2010.
Plan F enrollees accounted for about 51% of all Plan F enrollees in 2011, up from 47% in 2010.
Many plan types recorded a drop in the number of enrollees they covered and the share all Medigap users they covered.
One major plan type, Plan C, ended 2011 with 1.3 million enrollees, down 6.6% from the total recorded a year earlier.
Plan C's share of the Medigap market fell to 14%, from 16%.
In 1998, Plan C was the most popular Medigap plan type.