Objective To investigate the clinical characteristics of infectious mononucleosis(IM),the causes of misdiagnosis as acute tonsillitis and the methods to reduce misdiagnosis.Methods The data of 5 IM children who were mis-diagnosed with acute tonsillitis from February 2020 to January 2024 were retrospectively analyzed.Results Three patients were admitted to hospital with sore throat and fever for 2-4 d,and another 2 patients were admitted with sore throat for 3-5 d and neck swelling and pain for 2 d.All 5 patients were misdiagnosed with acute tonsillitis,and the misdiagnosis lasted 1-4 d.After receiving symptomatic supportive treatment for acute tonsillitis,5 patients did not improve,and IM was ultimately con-firmed by reexamination of the blood routine,throat swab culture and EB virus antibody detection.After confirmed diagnosis and symptomatic supportive treatment such as antiviral drug Acyclovir,the children recovered and were discharged from hospi-tal.Conclusion The clinical symptoms of IM are very similar to acute tonsillitis,and it is more likely to cause misdiagnosis.Improving doctors'clinical thinking ability and recognition of IM,mastery of the key points of differential diagnosis between IM and acute tonsillitis,and performance of relevant examinations are conducive to reducing the misdiagnosis rate.