Your biggest worry in the hospital isn't the condition that brought you there in the first place.

It's what else could go wrong while you're being "cured."

You could be poisoned with a drug overdose, sickened by hospital bacteria or even infected by a careless, dirty doc during a routine procedure--and don't think it can't happen to you.

It can--and as the latest studies show, it probably will if you spend enough time in a hospital.

One new study finds that nearly 20 percent of all hospital patients are harmed by their "care," and researchers say 63.1 percent of those mistakes are completely preventable.

Another new study puts a death toll on all those errors: The U.S. government says 15,000 hospitalized Medicare patients are killed by medical mistakes every single month.

That's 500 patients every day, or enough to make anyone think twice before heading to the emergency room.

In the first study, researchers looked at records on 2,341 patients admitted to one of 10 North Carolina hospitals between 2002 through 2007, and found that a quarter of them were victims of medical mistakes.

Many of those mistakes were serious, with 42.7 percent leading to extra time in the hospital. More than 8 percent of the cases were life-threatening, and 3 percent led to a permanent injury, including brain damage from a preventable post-surgical stroke.

And 2.4 percent of those medical mistakes caused or contributed to the patient's death, according to the study in the New England Journal of Medicine.

Common mistakes included the wrong drugs, overdoses of the right drugs, and infections that could have been avoided with simple good hygiene.

But what was most disturbing of all was that the researchers found no decrease in the number of errors over time--despite ramped-up efforts to improve hospital safety in recent years.

The researchers chose North Carolina because of the state's high level of health care, and say it's unlikely hospitals elsewhere are doing any better.

The other new study proves them right: The U.S. government says one in seven Medicare patients suffer from medical mistakes while hospitalized. That adds up to 134,000 injuries per month, including those 15,000 deaths I mentioned earlier.

And that's assuming hospitals are even telling the truth about their mistakes.

Eighty-seven California hospitals haven't reported a single significant error in at least three years--which could mean one of two things: These places should be copied by everyone else... or they're hiding something.

State officials are looking into it--and if it turns out these hospitals really are portraits of medical perfection, I'll be sure to share their secrets just as soon as I find out.

Just don't hold your breath waiting for that one.