Using a new and more detailed approach to diffusion tensor imaging (DTI) recently developed in our lab, the investigators hope to learn more about irregularities in the brain that are related to autism. The investigators are especially interested in brain regions that contribute to repetitive behaviors in children with autism. Repetitive behaviors include stereotyped motor movements (hand-flapping), self-injurious behaviors (head hitting), compulsions (lining up toys), insistence on things staying the same, and difficulty with change. These behaviors often interfere with learning, can disrupt daily functioning, and can lead to other behavioral problems. Two specific aims will be accomplished: