What is HMO? HMO stands for Health Maintenance Organization. This form of health insurance combines a range of coverages in a group basis. Doctors and other professionals are paid a flat monthly fee whether you see them or not. You pay the same amount every month, as long as you see doctors within the approved network. If you need to see a professional outside the network, you will first need a referral from a primary physician within the HMO, and then there may be additional fees to see a doctor outside of the network. Any visit, prescription, or additional care must be approved by the HMO in order to be covered. Kaiser Permanente is an example of an HMO.