The first two years of life is the most dynamic and perhaps the most critical phase of postnatal brain development. Concurrent with the rapid pace of structural brain growth is an equally rapid development of a wide range of cognitive and motor functions. In spite of its importance for understanding normal development and the early origins of neurodevelopment disorders such as schizophrenia and autism, our knowledge of human brain development in this crucial time period is minimal. While there has been growing interest in the study of normal brain development with MRI, most studies to date have not included the first few years of life because image acquisition and image analysis of children at this age is very challenging. We have addressed these challenges and have developed a rare prospective cohort of children who have already had neonatal MRIs.* In addition, we have developed novel and cutting edge, state-of-the-art image analysis techniques that provide powerful tools to study brain development in the first two years of life. We are one of the few groups in the world that has developed the expertise necessary to study very early brain development in children. We propose a longitudinal study of brain development with MRI in normal one and two year olds. This study will take advantage of a unique and large cohort of over 160 children who are enrolled in the currently funded study "Early Brain Development in High Risk Children" in which all subjects will have had prenatal ultrasounds and MRI's 2-4 weeks after birth and developmental follow-up at ages one and two years. Using novel automatic segmentation and parcellation methods, we will study regional changes in gray and white matter volumes over the first two years of life. The development of white matter tracts, including the corpus callosum and corticospinal tracts will be assessed using an innovative quantitative tractography of diffusion tensor imaging (DTI) properties and age-specific DTI atlases developed by our group. The maturation of diffusion properties in these white matter tracts can be directly compared to the myelination of the tracts through co-registration of DTI and structural MRIs. Regional brain growth over the first two years of life will be assessed with sophisticated three-dimensional brain mapping. Gender differences in the developmental trajectories of brain regions and white matter tracts will be assessed. Finally, we will study the changes in lateral ventricle shape in early childhood. The proposed study will provide critical, unavailable information about early brain development and will directly improve our understanding of brain normal development and provide the basis for future studies of neurodevelopment disorders in this age group.