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 1st 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 2nd part is more specifically devoted to CT [computed tomography] 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.