If I will only be exercising sport pilot privileges, do I need to renew an FAA medical certificate I now possess when it expires?
Response by the Federal Air Surgeon
No. You may use your current and valid U.S. driver's license to exercise sport pilot privileges; however, you must hold the required, valid FAA airman medical certificate if you wish to exercise private pilot (or higher) privileges. Also, if you are personally aware of an illness, then you have a duty to self-restrict from flying, and if there is any doubt, find and consult an AME.