We report on cytoarchitectonic neocortical findings in a patient with Williams syndrome (WS), a rare genetic disorder resulting in characteristic facies, heart defect, other connective tissue anomalies, and a unique neurobehavioral profile. Cytoarchitectonic anomalies include exaggerated horizontal organization of neurons within layers, most striking in area 17; increased cell packing density throughout brain regions; abnormally clustered and oriented neurons. Overall, posterior forebrain areas were markedly diminished in volume. The results suggest that brain anomalies may relate to the extreme visuospatial deficit in WS, the dysregulation of apoptotic cell death, and the genetic basis of WS, a hemizygous deletion including the elastin locus on chromosome 7. This case provides opportunities for linking brain findings to cognitive deficits and their genetic underpinnings.