PURPOSE: To measure the mean size of the various portions of the corpus callosum in normal Korean children, using MR imaging. MATERIALS AND METHODS: Our subjects were 166 children (male : female=100 : 66) aged under 15 whose findings on MR imaging and neurologic examination were normal. Using midsagittal T1-weighted imaging, we measured the length of the brain and corpus callosum, the height of the latter, and the thickness of its genu, body, transitional zone and splenium. The measurements were statistically analysed according to age and sex. RESULTS: Brain length and the size of the various portions of the corpus callosum tended to increase relatively rapidly during the first three years of life, but the rate of growth tended to decrease according to age. The mean length of the brain and corpus callosum and the mean thickness of the splenium of the corpus callosum did not differ according to sex. The mean thickness of the genu, body and transitional zone of the corpus callosum was greater in males than in females. The ratio of the length of the corpus callosum to the anteroposterior diameter of the brain was significantly greater in females than in males (alpha = 0.05). CONCLUSION: Using MR imaging, we measured the mean sizes of the various portions of the corpus callosum in normal children ; these values may provide a useful basis for determing changes occurring in its structure.