Health maintenance organizations are prepaid health plans. As an HMO member, you pay a monthly premium. In exchange, the HMO provides comprehensive care for you and your family, including doctors' visits, hospital stays, emergency care, surgery, lab tests, x-rays, and therapy.

The HMO arranges for this care either directly in its own group practice and/or through doctors and other health care professionals under contract. Usually, your choices of doctors and hospitals are limited to those that have agreements with the HMO to provide care. However, exceptions are made in emergencies or when medically necessary.

There may be a small co-payment for each office visit, such as $5 for a doctor's visit or $25 for hospital emergency room treatment. Your total medical costs will likely be lower and more predictable in an HMO than with fee-for-service insurance.

Because HMOs receive a fixed fee for your covered medical care, it is in their interest to make sure you get basic health care for problems before they become serious. HMOs typically provide preventive care, such as office visits, immunizations, well-baby checkups, mammograms, and physicals. The range of services covered varies in HMOs, so it is important to compare available plans. Some services, such as outpatient mental health care, often are provided only on a limited basis.

Many people like HMOs because they do not require claim forms for office visits or hospital stays. Instead, members present a card, like a credit card, at the doctor's office or hospital. However, in an HMO you may have to wait longer for an appointment than you would with a fee-for-service plan.

In some HMOs, doctors are salaried and they all have offices in an HMO building at one or more locations in your community as part of a prepaid group practice. In others, independent groups of doctors contract with the HMO to take care of patients. These are called individual practice associations (IPAs) and they are made up of private physicians in private offices who agree to care for HMO members. You select a doctor from a list of participating physicians that make up the IPA network. If you are thinking of switching into an IPA-type of HMO, ask your doctor if he or she participates in the plan.

In almost all HMOs, you either are assigned or you choose one doctor to serve as your primary care doctor. This doctor monitors your health and provides most of your medical care, referring you to specialists and other health care professionals as needed. You usually cannot see a specialist without a referral from your primary care doctor who is expected to manage the care you receive. This is one way that HMOs can limit your choice.

Before choosing an HMO, it is a good idea to talk to people you know who are enrolled in it. Ask them how they like the services and care given.