Autism may be due to an abnormal development of a neural network involving-several regions of the brain. The proposed project will be the first to directly examine white matter connectivity in autism. It has been suggested that the dysfunction in the frontal lobe may relate to the characteristic speech problems and that dysfunction in the limbic system, may be one of the mechanisms responsible for the emotional and executive function symptoms of the illness. Compared to control subjects, in the patients with autism the anterior cingulate gyrus, which is a part of the limbic system, showed decreased metabolic rate and structural changes. The anterior cingulate gyrus communicates with many other areas of the brain to coordinate complex behaviors. Communications from this area travel through the axons or white matter of the brain. The axons from the cingulate cortex form the cingulum and this sheaf of communication sweeps up and out of the cingulate. Failure of this communication bundle to systematically find its targets and instead to develop as a tangled and misrouted jumble may explain the disordered executive function and impaired emotional processing in autism. Diffusion tensor imaging makes it possible for the first time to image the direction and alignment of axons in the brain's white matter. This new technique provides a unique opportunity to directly examine quality of white matter connectivity between key brain regions. We propose to collect diffusion tensor MRI scans, anatomical MRI's and PET scans in 30 adult patients with autism spectrum illnesses and 30 healthy control subjects. In the current project along with the cingulum, we will examine the white matter organization in the cerebellar peduncles, striatum, corpus callosum and frontal white matter and will correlate our findings with the clinically distinct presentations of autism spectrum illnesses.