Sex and handedness differences in the volumes of cerebral ventricles were studied in 20 right- and 21 left-handed subjects. To assess the volumes of cerebral ventricles, Cavalieri's method was used using MRI. In right-handers, the volume of the lateral ventricle was higher in the right side than in the left side, but, in left-handers, it was higher in the left side than in the right side. The volumes of right-lateral and third ventricles were larger in right-handers than in left-handers. There were no sex related differences in terms of the volumes of right- and left-lateral, third, and fourth ventricles. These results suggest that left-handedness is an important factor reducing the sizes of all the brain ventricles.