Controversy exists in the neuropsychological literature concerning the existence of gender-associated differences in cognitive functioning and in hemispheric lateralization of cognitive functions. A recent study, based on 14 brains obtained at autopsy, reported sex differences in the splenium of the human corpus callosum and suggested that the larger splenium in females reflects less hemispheric lateralization, or "specialization," than the male brain for visuospatial functions. Our measurements of the human corpus callosum using magnetic resonance images of 37 living subjects failed to confirm reported sex differences in the splenium. A marginally significant sex-related difference in minimum body width and an age-related decrease in anteroposterior distance were found. Most striking were the large variations in callosal size and shape among individuals regardless of age or gender. Existing knowledge of the functions of the corpus callosum does not permit correlations between variations in callosal size and shape and variations in cognitive functions.