Background： Infectious mononucleosis is a disease precipitated by Epstein-Barr virus(EBV) in mostly children, some seronegative adolescents and young adults comprising clinical symptoms such as fever, lymphadenopathy, and pharyngitis as well as laboratory findings such as hetero-phil antibodies and atypical lymphocytosis. It is confirmed by serologic test for EBV. Materials and Methods： A retrospective evaluation of 26 patients who diagnosed with infectious mononucleosis was peformed through the analysis of typical symptom, sign and laboratory findings. Results : Infectious mononucleosis occurs mostly at 3 to 10 years (74.9%), common symptoms and signs are fever, cervical lymphadenopathy, tonsillar enlargement and exudate. Positive ratio of atypical Lymphocyte(>10%) and hetrophil antibodies are 61.5%, 35.2% respectively, it is less diagnostic. EBV-viral capsid antigen(VCA) IgM are positive in all cases, so it is most diagnostic findings. Conclusion： Infectious mononucleosis should be considered as a cause of cervical lymphadenopathy and pharyngotonsillitis in children and young adults, the assessment of EBV-VCA IgM is necessary for the diagnosis.