Original Medicare is a fee-for-service program. This means that you can go to any doctor or other healthcare provider who accepts Medicare, and that provider will get paid for that service by Medicare. Below are some of the differences between Original Medicare and Medicare Private Fee-for Service (PFFS) plans. 

• PFFS plans must have a limit on out-of-pocket costs. The out-of-pocket limit can be high but may help protect you if you need a lot of health care or need expensive treatment.
• Out-of-network doctors may refuse to treat you because they do not accept your plan. Even if the doctor has treated you before, providers outside of the network can decide whether or not to treat you before each service. (Note: for emergency or urgent care, you must pay what you would have paid from a plan provider or $65, whichever is less).
• PFFS plan networks are measured geographically. There may be more than one PFFS plan network in your area and each plan network might have different costs. In Original Medicare, the benefits and costs are uniform nationally.
• PFFS plans can decide to stop offering coverage or to change their benefits package on a yearly basis.
• PFFS plans may offer benefits that Original Medicare does not cover, such as dental care, but you will likely have to pay more.
• Many people who have Original Medicare also purchase a Medigap plan to help pay some of their costs (such as deductibles and copays). Medigap plans are supplemental insurance policies that work specifically with Original Medicare. You cannot have a Medigap and a Medicare PFFS plan together.