Tonsillitis is an inflammation of the tonsils, a tissue at the back of the throat. Most cases of tonsillitis are caused by a virus, although it can also be caused by a bacterium.
This inflammation most commonly affects children between preschool ages and mid-teenage years. Surgery to remove tonsils is usually performed only when it occurs frequently.

The most common symptoms of tonsillitis vary from swollen tonsils and sore throat to difficulty when swallowing and fever, although it is also normal to have a scratchy voice, stomach-ache, stiff neck and headache.