HMOs (Health Maintenance Organizations) and PPOs (Preferred Provider Organizations) differ in three key ways:

1. Medicare PPOs must cover your care if you use doctors and hospitals outside the network, although they usually charge you more if you do. In an HMO you generally cannot see doctors or providers who are out of network.
2. Medicare PPOs generally charge higher monthly premiums than Medicare HMOs.
3. Medicare PPOs cannot require that you see a primary care physician before going to a specialist.