This grant provides support for an NIH Autism Center of Excellence (ACE). On the basis of structural magnetic resonance imaging (sMRI) and head circumference studies, it is now well established that brain size is often enlarged in autism. Most evidence also indicates that white matter volume (consisting mostly of axons in the brain) is disproportionately enlarged compared to gray matter volume, and new data from functional MRI (fMRI) and diffusion tensor imaging (DTI) studies of ASDs have shown alterations in "functional connectivity" among people with ASDs. This study proposes to characterize cerebral white matter abnormalities in the ASDs, both in terms of alteration in its total volume using sMRI and through the use of DTI. This anatomical information will be correlated with fMRI functional connectivity data to look at the relationship between volume and quantitative and dynamic measures of functional connectivity.