The morphological structure of the postcentral sulcus and its variability were investigated in 40 structural magnetic resonance images of the human brain registered to the Montreal Neurological Institute (MNI) proportional stereotaxic space. This analysis showed that the postcentral sulcus is not a single sulcus, but rather a complex of sulcal segments separated by gyri, which merge their banks at distinct locations. Most of these gyri are submerged deep within the sulcus and can be observed only by examining the depth of the sulcus, although a small proportion may be observed from the surface of the brain. In the majority of the examined cerebral hemispheres (73.75%), the postcentral sulcus is separated into two or three segments or, less frequently, into four or five segments (12.5%), or it remains continuous (13.75%). Examination of the in-depth relationship between the postcentral sulcus and the intraparietal sulcus revealed that these two sulci may appear to join on the surface of the brain but they are in fact always separated by a gyrus in the cortical depth. In 32.5% of the examined hemispheres, a dorsoventrally oriented sulcus, the transverse postcentral sulcus, is located anterior to the postcentral sulcus on the lower part of the postcentral gyrus. Systematic examination of the morphology of the postcentral sulcus in the proportional stereotaxic space that is used in functional neuroimaging studies is the first step toward the establishment of anatomical–functional correlations in the anterior parietal lobe. J. Comp. Neurol. 518:3701–3724, 2010. © 2010 Wiley-Liss, Inc.