While HMO benefits are generally more comprehensive than those of traditional fee-for-service plans, no health plan will cover every medical expense.

Very few plans cover eyeglasses and hearing aids because these are considered budgetable expenses. Very few cover elective cosmetic surgery, except to correct damage caused by a covered accidental injury. Some fee-for-service plans do not cover checkups. Procedures that are considered experimental may not be covered either. And some plans cover complications arising from pregnancy, but do not cover normal pregnancy or childbirth.

Health insurance policies frequently exclude coverage for preexisting conditions, but, as explained, federal law now limits exclusions based on such conditions.

You should also remember that insurers will not pay duplicate benefits. You and your spouse may each be covered under a health insurance plan at work but, under what is called a “coordination of benefits” provision, the total you can receive under both plans for a covered medical expense cannot exceed 100 percent of the allowable cost. Also note that if neither of your plans covers 100 percent of your expenses, you will only be covered for the percentage of coverage (for example, 80 percent) that your primary plan covers. This provision benefits everyone in the long run because it helps to keep costs down.