According to the Columbia Electronic Encyclopedia, Adenoids are "the common name for the pharyngeal tonsils, spongy masses of lymphoid tissue that occupy the nasopharynx, the space between the back of the nose and the throat.
Normally the adenoids, like the palatine tonsils (tonsils) located on either side of the throat, help prevent infection in the surrounding tissues. However, if they become enlarged they can interfere with normal breathing and even sometimes with hearing. When severely enlarged, adenoids can even affect normal dental development and possibly impact facial expression.
Infection of the adenoids is common, the symptoms resembling those of tonsillitis, with which it is frequently associated. Surgical removal of the adenoids is advisable when enlargement and repeated infection interfere with development and health."