From http://www.theabpm.org/

For those ABPM board certified:
Some licensing boards are now requiring maintenance of certification (MOC)  for all renewals even for individuals with lifetime certifications.  In addition beginning in August 2011, all ABMS member boards will be required to report the MOC participation status of all diplomates, including those with lifetime certificates. A letter from ABPM to diplomates is here  click here .

Registering for MOC is easy and costs 200 dollars. The current requirements are here –
https://www.theabpm.org/moc/moc_requirements.cfm. As a quick summary you need to be licensed, to take MOC and CME credits, to take a cognitive test in years 7 to 10 and to provide an assessment of practice performance which can include a portfolio for those who don’t see individual patients.