HMOs provide medical treatment on a prepaid basis, which means that HMO members pay a fixed monthly fee, regardless of how much medical care is needed in a given month. In return for this fee, most HMOs provide a wide variety of medical services, from office visits to hospitalization and surgery. With a few exceptions, HMO members must receive their medical treatment from physicians and facilities within the HMO network. The size of this network varies depending on the individual HMO.

When you join an HMO, you choose a primary care physician (PCP) who is your first contact for all medical care needs. The primary care physician provides your general medical care and must be consulted before you can see a specialist. Because of this control system, HMO costs tend to increase less rapidly than other insurance plans.