Acute tonsillitis is a common condition and usually runs a benign course. However life-threatening complications do still occur, even in this postantibiotic era. Infection can spread downwards into the mediastinum through the anatomic cervical spaces, causing widespread cellulitis, necrosis, abscess formation and sepsis. We present a case of descending mediastinitis in an 18-year-old woman, arising from her first episode of tonsillitis and treated successfully by surgical drainage. We believe that an awareness of this complication, early diagnosis using computed tomography scanning, and prompt, adequate surgical drainage will reduce morbidity and mortality.