We have recently developed a computer program for measuring midsagittal sections of the human corpus callosum, similar to one used for the rat. Callosal area, perimeter, axis length, and 99 widths for 104 subjects were entered into a factor analysis in order to define regional clusters. Seven width factors were obtained. Regional widths were found to be sensitive to Sex X Handedness interactions in the anterior body, with right-handed females and left-handed males being larger. In the posterior body males had wider callosa than females. A further analysis within the 'isthmus' region compared consistent and non-consistent right-handed males and females. Consistent right-handed males and both female groups had smaller callosa than non-consistent right-handed males. These findings confirmed the use of consistency of handedness as an important independent variable with respect to human callosal morphology.