Receiving Social Security means you get Medicare whether you want it or not. It gets taken out of your check automatically after your 25th month of disability:

When & how to sign up for Part A & Part B | Medicare.gov

krisaskira is correct I think in that you do have to pay Medicare Premiums unless you're on SSI or receive too little--then the government pays your premiums.

badmouse, do you have both part A and B? You don't have to accept Part B (doctors) and you can elect to only have Part A (hospital coverage). I don't think you have to pay premiums on just Part A (from what I remember, but you can double check that with SSA). If you're paying for Part B coverage (which is optional) you can contact SS and tell them you don't want it anymore. When I got my first card they automatically enrolled me in Part B and I saw what the preimuims were, so I told them I didn't want it. (It turned out since I receive SSI, my premiums would be paid so I kept it), but you don't have to keep Part B. Just make sure the doctors at the clinics will still take you.