The gender difference of corpus callosum is a long standing controversy. Some investigators have reported that adult females have a more bulbous splenium and larger area relative to brain size, but others failed to replicate this. Few studies have reported on sexual dimorphism during development. Midsagittal ultrasonographs were obtained through the anterior fontanelle of healthy Korean neonates (100 males, 100 females) and were analyzed with NIH Image. The total area of corpus callosum and sub-regions of corpus callosum showed no gender differences. However, the male corpus callosum had significantly more height than that of the female whereas there was no difference in width of the corpus callosum. The estimated average thickness of corpus callosum was greater in the female splenium.