An abscess behind the tonsils that pushes one of the tonsils toward the uvula (the prominent soft tissue dangling from the back of the palate in the back of the mouth). A peri- tonsillar abscess is generally very painful and asso- ciated with difficulty opening the mouth. If a peritonsillar abscess is untreated, the infection can spread deep into the neck, causing airway obstruc- tion and other life-threatening complications.