Abstract： Objective To determine the proportion and the clinical value of the thymus extending superiorly into the lower neck in children.Methods The MR images of 400 normal children were retrospectively reviewed.According to the childhood staging criteria.all children were divided into four groups:the infancy and toddlerhood group(0-3 yo,42),the pre-school age group(>3-6 yo,87),the school age group(>6-12 yo,168),and the adolescence group(>12-18 yo,103).The presence or absence of the superior extension of the thymus above the manubrium Was determined on sagittal T2-weighted images.If so,the distance between manubrium and thymic apex was measured.The associations between frequency of ccrvicaI extension and age and sex were evaluated using correlation analysis.Results Superior extension of the thymus was detected in 288(288/400,72.0%)children,with 39(39/42,92.9%)in the infancy and toddlerhood group,72(72/87,82.8%)in the pre-school age group,118(118/168,70.0%)in the school age group,and 59(59/103)in the adolescence group(57.3%).There Was a statistically significant relationship between age group and frequency of cervical extension of the thymus (X2=4.9684,P<0.05).There was no significant decreasing trend in the mean distance of cervical extension between age increasing groups(F=2.28,P>0.05).Conclusions Cervical extension of the thymus occurs in the majority of children,and should be considered as a normal finding.Through recognizing this finding,doctors can avoid misdiagnosing it as a pathologic mass.