Not all doctors take medicaid or medicare and the law does not require doctors to accept them. Doctors who opt out of medicare and medicaid cite reasons such as reimbursement being too low and the paperwork too much of a hassle. If you have medicare and the doctor has opted out, medicare may pay for some of the expenses but it is on you to pay the difference. Therefore, it is important to ask a doctor if (s)he is participating in Medicare. To find a participating doctor in your area, you can also check the medicare website (medicare.gov).