Tonsils are the two masses on the back of the throat.
Tonsils and adenoids are near the entrance to the breathing passages where they can catch incoming germs, which cause infections. Scientists believe they work as part of the body's immune system by filtering germs that attempt to invade the body, and that they help to develop antibodies to germs. This happens primarily during the first few years of life, becoming less important as we get older. Children who must have their tonsils and adenoids removed suffer no loss in their resistance. Tumors are rare, but can grow on the tonsils.