Infectious mononucleosis causing upper airway obstruction due to tonsillar disease and associated lymphadenopathy in adolescents is well recognized. However, infection with Epstein-Barr virus (EBV) in a young child of six months is rare. The authors present such a case, with massive swelling of the retropharyngeal lymph nodes, that has not been published previously. The patient presented to this department with a short history of an upper respiratory tract infection and mild upper airway obstruction. On examination there was a massive enlargement of the retropharyngeal space with a compromised airway. This was confirmed on X-ray. She made an uneventful recovery following incision and drainage and a short period of endotracheal intubation. Because of the presence of retropharyngeal lymphoid tissue in infancy an alternative site of upper airway obstruction may occur here in this age group.