Nearly 100 have been reported since this problem first surfaced several weeks ago.
The main link - all the patients report vaping before being hospitalized. Some patients have shortness of breath and chest pain and some are in intensive care.
Researchers are still trying to determine what's causing the illness.
Some believe it could be linked to a fungus or bacteria that was found in some brands of E-cigarette liquid.
Others say the chemicals themselves could be to blame. Many were never tested for inhalation safety.
Report: 3 Illinois vaping teens in hospitals