Magnetic Resonance Imaging (MRI) reveals anatomical asymmetries of the sulcal demarcation of the posterior operculum from the parietal cortex that correlate with handedness in normal subjects. The sulcal demarcation is greater on the right in most right handers, but evenly distributed in left handers. This in vivo asymmetry corresponds to the commonly larger planum temporale on the left side. Hand Preference, Hand Performance, Dichotic Listening and Visual Field Preference measures were correlated with several measures of anatomical asymmetries seen on MRI. The sulcal demarcation, anterior frontal width and parietal width correlated best with hand performance, as measured on a dot tapping task. The biological significance of the distribution of anatomical and functional asymmetries is discussed.