Purpose: To measure the size of normal corpus callosum in each portion using objective and reproducible methodwith MRI and evaluation of morphological change of corpus callosum by grade of hydrocephalus. Materials andMethods: Midsagittal T1-weighted MR imaging of the corpus callosum was investigated in 41 volunteers of normalKorean adults and 19 patients with hydrocephalus. Corpus callosum was measured for the anteroposterior length(A),height(B), and the thickness of genu(C), body (D), splenium(E), and the narrowest portion of body(F). And theanalysis of morphology and signal intensity of the corpus callosum were also evaluated. Hydrocephalus was gradedas mild, moderate, and severe, and comparision of thickness with normal corpus callosum in each poriton was done.Results: The mean length and height were 72.3mm, 28.6mm in male, and 70.7mm, 28.9mm in female. And the meandiameters for C,D,E, and F were 13.1mm, 8mm, 13.2mm, 5.2mm in male, and 12.8mm, 7.5mm, 12.3mm, 5mm in female. Themorphology of normal corpus callosum was "hook" shaped on midline sagittal T1-weighted image. Narrowing atposterior third portion of body were present on 30 cases(73.2%) and even in thickness of the body in 11cases(26.8%). The signal intensity of the corpus callosum on midsagittal T1-weighted spin echo image of normalcases was homogeneous hyperintense as compared with cerebral gray matter. In hydrocephalus, A and B were increasedand other portions were decreased in thickness. Genu and the narrowest portion of body showed significantdifference of thickness according to the grade of hydrocephalus. Conclusion: The mean dimention of all portion ofcorpus callosum were larger in male than female except for callosal height but not significant statistically withthe exception of splenium. Hydrocephalus lead to morphological change of the corpus callosum. Among the portion ofcorpus callosum, genu and the narrowest portion of the body were thought to be the most sensitive indicators ofdegree in hydrocephalus.ocephalus.