The head circumference of some patients with autism has long been known to be larger (Davidovitch et al., 1996; Woodhouse et al., 1996; Fombonne et al., 1999; Miles et al., 2000) because of abnormal acceleration in growth in early infancy (Courchesne et al., 2003). While no studies have been published on the neuroanatomy of high-risk individuals before a diagnosis of autism is made, retrospective data have shown that children with macrocephaly and autism do not have increased head circumference at birth (Lainhart et al., 1997; Courchesne et al., 2003; Dementieva et al., 2005; Redcay and Courchesne, 2005) but begin to show larger head measures at about 4 months of age (Gillberg and de Souza, 2002; Courchesne et al., 2005; Redcay and Courchesne, 2005). These findings suggest that autism may be underlain by either problems in early postnatal life and/or processes of embryonic development on which these postnatal events depend. Structural imaging of individuals with autism has shown that differences in brain volume, including both white and gray matter, diminish after the age of 5 years (Hazlett et al., 2005), although some studies have reported increases in gray matter volume in adolescents and adults with ASD (Lotspeich et al., 2004; Palmen et al., 2005; Hazlett et al., 2006), particularly in PFC (Mitchell et al., 2009).