The study released by the school of medicine at Northwestern University Monday found that illiterate patients have daunting problems when it comes to following medication instructions, hospital forms and even appointment slips.

"When patients can't read, they are not able to do the things necessary to stay healthy," said Dr. David Baker, a lead author of the study published this week in "Archives of Internal Medicine. "They don't know how to take their medications correctly, they don't understand when to seek medical care, and they don't know how to care for their diseases."

The 10-year study followed 3,260 Medicare patients in Ohio, Florida and Texas who took part in a literacy test using pill bottles and other health-related materials.