Eighty normal adults were studied with MRI to investigate the relationship between regional morphology of the corpus callosum and characteristics such as age, gender, education, and cranial size. The variability coefficient was 20% in total callosal area and from 19% to 40% in regional callosal area. Increasing age and smaller cranial area were both associated with smaller total and regional callosal areas; there were no effects of gender and education. The relative effects of age and cranial size varied across regions and were most prominent for anterior subdivisions. However, age and cranial size together explained less than half the variance in regional callosal size. Further study is needed to identify additional correlates of regional callosal anatomy.