To date, the unifying pathogenesis, or etiology, of autism spectrum disorders (ASDs) and Williams syndrome (WS) remains unknown, partly because of the broad variation of phenotypes and the heterogeneity of syndrome expression. In particular, in order to comprehend the etiological mechanisms of their characteristic behaviors, great importance should be placed on realizing how the neural networks of individuals with autistic disorders and WS are formed and work. As such, in this paper, cortical network abnormalities, based on data from a variety of research fields, are presented: psychopathological, histopathological, and clinicopathological studies, as well as structural (i.e., morphological) and functional magnetic resonance imaging studies, including functional connectivity analysis. Based on the structure of the network, we propose an etiology for ASD and WS. Finally, we explain a variety of symptoms of these two disorders, including social and nonsocial dysfunction, based on our proposed neural network.