Infectious mononucleosis (IM) is a benign lymphoproliferative disorder primarily caused by the Epstein-Barr virus (human gamma-herpesvirus 4) and most commonly affects 15-24-year-old individuals. Spontaneous splenic ruptures occur in 0.1% to 0.5% of patients with IM and can be life-threatening despite reports of suppurative processes involving the tonsils, such as intra-amygdala or peritonsillar abscesses. However, these rare complications can easily be misdiagnosed as acute suppurative tonsillitis caused by typical bacterial infection. This paper reports a case of a teenager with IM and concurrent suppurative tonsillitis, who was initially misdiagnosed with acute bacterial tonsillitis and failed to respond to antibiotic treatment. Examination confirmed IM combined with suppurative tonsillitis. Notably, his symptoms improved significantly after antiviral treatment. Therefore, we suggest that IM-complicating suppurative tonsillitis should be excluded when acute suppurative tonsillitis does not respond to antibiotic treatment and antiviral treatment strategies are urgently needed to avoid serious life-threatening complications.