If you've ever spent time in a hospital, you've almost certainly been overcharged. “There is no way to avoid being overbilled. It is going to happen. In the last several years of looking at hundreds of bills, Ive run across only one hospital bill with no errors,” says Edward Waxman of Edward R. Waxman & Associates, an independent hospital bill auditor with 10 years of experience helping consumers sort through their medical bills.

Overcharges hurt the most when they are not covered by insurance, but even when they are, they can impact your pocketbook or your health.

They inflate co-pays and—even more important if you will ever face treatment for an expensive chronic condition—they eat up your insurance benefits, making the day when you max out your policy that much closer.

Often, erroneous charges are obscured by billing codes and "medicalese." In one case, a 60-year-old obese man with chronic obstructive pulmonary disease and congestive heart failure was admitted to the hospital for a 57-day stay. The bill was $138,345. Waxman audited it, noting a daily charge of $202.75 for “MAGNUM II BA.” A drug? A lab test? Nope. It was the name of a heavy-duty bed designed for overweight patients. Hospitals are not allowed to charge for reusable equipment like beds, so Waxman disputed it. The hospital took the charge off the bill—resulting in a total reduction of $11,556.75.

Here are some steps to take to protect yourself against paying more than you should.

Talk to your hospital about the bill ahead of time.

If you're paying your own way for an expensive medical procedure like a coronary bypass, go in advance and ask to speak to the chief financial officer of the hospital, advises Gerard F. Anderson, a professor of health policy and management at the Johns Hopkins Bloomberg School of Public Health. You might not reach that person—more likely, you will be passed to a manager in the financial department—but speak to the highest-level official you can. Hospitals, which usually charge three or four times the cost of their services, routinely accept discounted payments from insurers and Medicare, so they may be persuaded to give you a break too. “Say, ‘Im willing to pay a little bit more than what Medicare pays. Often they will give you a substantial discount—30% or more,” says Anderson.

Keep a log.

To the extent that you're able, write down the dates of your hospital procedures and medicines that you're given, so you have something to check the bill against later. “If you have an accountant mentality and you're awake enough to be able to do that, that's great, but the reality is that many people cant,” says Louis Saccoccio, executive director of the National Health Care Anti-Fraud Association. If you're too weak to do it yourself, assign a friend or family member to the task.

Pack your own drugs.

Take your over-the-counter and regular prescription medications with you. “In the hospital, the nurse has to put it in a plastic cup and walk it down the hall to you—you may pay $3 or $5 for an aspirin,” says Waxman. Prescription drugs, of course, can be much more, and can add up during a long stay. Bring any that you are taking regularly in their original pharmacy bottles. Be sure to tell your nurse what you are taking, and check your hospital and doctor's bills carefully after treatment to make sure you weren't charged for the medication anyway.

Double-check your personal information on file with the hospital and your insurer.

An incorrect social security number, name, address, or date of birth can result in accidentally being charged for someone else's treatment. Also: “Be very careful of your insurance card. Make sure no one gets hold of it or makes copies of it unnecessarily. Someone could try to use it to get health-care services,” says Saccoccio. Victims of what is now termed medical identity theft have found their health-insurance lifetime limits exhausted after their accounts were billed for services they never received. The Federal Trade Commission measured statistics on medical identity theft for the first time in November 2007, finding approximately 250,000 victims in 2005. Health-care employees, not random thieves, are thought to be responsible for most stolen insurance numbers, but you can help protect yourself by guarding your insurance information closely. Since you will have to present your insurance card when you are admitted to the hospital or go to a doctor's appointment, be vigilant about checking your bill and making sure it doesn't include any fraudulent charges that may have stemmed from an inside job.

Order an itemized statement.

Many hospitals send a summary of charges, but you have a right to ask for the complete breakdown. Look at the line charges and the diagnostic codes. These can be hard for the average person to understand, but if something looks fishy, ask the billing department to explain it. If you have a bill of $10,000 or more, however, consider hiring a professional bill auditor, Waxman advises.

Read your explanation of benefits (EOB).

Your insurer will send you a letter that explains exactly what was paid, and how much you are responsible for. Compare it with the hospital bill. Though the medicalese may be hard to understand, at least check the dates for accuracy. “If you were in the hospital overnight, and a month later you get an EOB that says the hospital stay was four days, then obviously something is wrong,” says Saccoccio. If you kept a log during your stay, compare it against the services and medicines on your EOB. If there are discrepancies, ask your health plan to review your hospital bill.

Enlist help from the state.

If you are held responsible for charges that you think are erroneous, contact the consumer protection office of the state attorney generals office for help. Visit the website of the National Association of Attorneys General to find the phone number for the attorney general's office in your state.

Consider hiring help.

Medical billing advocates charge an hourly fee (about $25), or take a percentage of recovered money, to audit your medical bills and negotiate with health-care providers. If you have a very large set of confusing bills and think there may be errors, this can be a time-saving option. You can find a professional through Medical Billing Advocates of America, a network of 61 medical bill auditing companies across the country.

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