If you have insurance coverage through an HMO, you have to choose a primary care doctor within the plan’s network — who will coordinate your care and refer you to a specialist (within the network) when it’s necessary.
The doctors in the HMO network will typically be in your local area. If you see a provider outside the network (unless it’s an emergency), you pay the FULL cost.
Some HMOs do not have a monthly premium besides the standard Medicare Part B premium. Different HMO plans will have different networks of providers, as well as different copays and coinsurance. Many HMOs include prescription drug (Part D) coverage.