Life-threatening upper airway obstruction can be caused by tonsillopharyngitis secondary to infectious mononucleosis (IM). The administration of corticosteroids, emergency tracheostomy and acute tonsillectomy have been advocated as ways of managing this problem. In a series of 25 patients admitted over a five-year period with IM, 15 were judged to have symptoms severe enough to warrant the administration of corticosteroids. Six of these 15 patients had little improvement in their condition and thus underwent acute tonsillectomy. There were no significant complications of this surgery. A further three patients who received corticosteroids required tonsillectomy for recurrent tonsillitis later in the study period. By contrast, only one of the ten patients who did not receive corticosteroids subsequently required tonsillectomy. Acute tonsillectomy is of value in selected cases of IM tonsillopharyngitis. It may decrease the morbidity of recurrent tonsillitis after IM, in addition to averting the immediate risk of respiratory obstruction.