The first question, if a person is interested in joining a prepaid plan, is whether his or her employer offers that as an alternative to conventional health insurance. If not, the person may not be interested in paying the full cost of a plan out of his or her own pocket.

If the person is self-employed, he must apply for membership in a local HMO and, depending on his health and whether or not the plan is accepting members, he may or may not get in.

If the person's employer offers HMO membership, then all that is needed is to fill out an application in most cases. After about a month - or sometimes less than a week - the applicant and his family are enrolled.

Once enrolled, a HMO member choose his or own physician within the HMO. There is no guarantee that a patient will always see his own physician, especially when an appointment is made on short notice.

But many HMOs encourage patients to choose their own physician, try to see him regularly and, if not satisfied, to choose another physician. However, they may not consult physicians outside the plan without permission or referral and expect the plan to cover the cost.

Coverage varies from plan to plan, but most of the comprehensive plans offer all necessary medical and hospital care at no cost beyond the premium. Some plans charge a nominal fee for office visits and some charge more than a nominal fee for obstetrics.

The most misunderstood aspect of a prepaid plan is that members are limited to physicians within the plan. A prepaid plan is not just another form of insurance that leaves a member fee to choose any physician in the community for treatment.