Referring to bicommissural coordinates, 10 human brains fixed within their own skull were examined for right-left differences of the posterior Sylvian cortex, a region known to bear the most striking gross anatomical asymmetries. In the first part of the study a millimetric assessment of right-left differences in this region was carried out using life-size lateral photographs of each hemisphere. The second part is more specifically devoted to CT recognition of these cortical areas: Each hemisphere was cut into horizontal, frontal, or sagittal slices in which some cortical landmarks were analyzed to allow accurate CT identification of gyri and sulci showing the most asymmetrical features. This work provides an anatomical framework for correlative studies dealing with cerebral dominance.