The specific is to study the MR morphologic and spectroscopic brain correlates and predictors of development in children with severe developmental disorders (autistic spectrum disorders and/or mental retardation and/or language disorders). Given the frequently observed association of autism with known medical conditions, particularly in cases with comorbid mental retardation and in cases with atypical autism (Rutter et al., 1994; Gillberg, 1995), children with suspected autism or related developmental disorders will be asked to participate in an extensive state of the art laboratory work-up which includes T1 and T2 weighted MRI of the brain. MRI data will be analyzed both qualitatively, looking for focal abnormalities and degree of myelination, and quantitatively, measuring volumes of total brain, cerebellum, ventricles and grey and white matter. For research purposes, the work-up will be supplied with proton Magnetic Resonance Spectroscopy (MRS) of the brain. This data set provides the opportunity to chart brain-behavior relationships in young children with suspected autism and related PDD cross-sectionally.