Objective To investigate atypical lymphocyte and lymphocyte subsets in children with infectious mononucleosis(IM)and its relationship with the clinical symptoms by retrospective method.Methods Two hundred and six children were diagnosed as infectious mononucleosis.Atypical types,lymphocyte subsets,and clinical symp-toms and their relationship were evaluated and analyzed.Results In the IM children CD +3 increased,CD +3 CD +4 decreased,CD +3 CD +8 increased and NK cells decreased.The control group was (64.23 ±6.26 )%,(32.96 ± 8.68)%,(20.25 ±7.45)%,(14.68 ±5.4)%,the IMgroup was (84.13 ±14.64)%,(18.45 ±5.14)%,(54.46 ± 16.82)%,(4.65 ±1.50)%,the difference was statistically significant(P <0.001).92.9% patients had more 10%atypical lymphocytes.The children with more than 20% atypical lymphocytes had higher CD +3 CD +v8 and NK cells decreased,(58.78 ±16.67)%,(3.28 ±1.57)%.The difference with the atypical cells more than 10% less than 20% and the group less than 10% has statistically sighnificant which were (54.53 ±15.12)%,(4.55 ±1.64)%, (50.25 ±14.23)%,(5.13 ±1.84)% (P <0.001).The serious type of IM children had higher ratio of increased CD +3 CD +8 and decreased NK cells and had statistically significant compared with the light group,which were (57.78 ± 15.45)%,(3.18 ±1.61)%,(51.09 ±12.26)%,(4.68 ±1.82)%,(20.25 ±7.45)%,(14.68 ±5.46)%(P <0.001).Conclusion The infectious mononucleosis can cause abnormal immune functions.The ratio of atypical lym-phocytes,CD +3 ,CD +3 CD +4 ,CD +3 CD +8 and NK cells numbers can be viewed as a monitoring index of the disease.