Williams syndrome (WMS) is a genetic condition resulting from a hemideletion on chromosome 7 that causes cognitive impairment, and a variety of growth and physical abnormalities. Little is currently known about brain morphology in WMS, although one recent MRI report suggested that the central sulcus was abnormally short on its dorsal end compared to normal IQ controls. We sought to replicate this finding in a group of 28 persons with WMS in comparison to both an age and sex matched normal IQ control group (n = 22). In addition, we sought to test the specificity of this finding by a further comparison to an IQ matched control group (n = 20). Using high resolution isotropic voxel MRI, the dorsal and ventral extension of the central sulcus was traced and the distance from the interhemispheric and sylvian fissures was measured. The dorsal extension of the central sulcus in both hemispheres was significantly more distant from the interhemispheric fissure in WMS compared to the lower IQ group and to the normal control group (p's < 0.001). There was no significant difference between groups in the ventral end of the central sulcus. These results suggest that the abnormal dorsal end of the central sulcus may be a specific characteristic of WMS not shared with general mental retardation or low IQ.