Childhood psychiatric disorders are rarely static; rather they change over time and longitudinal studies are ideally suited to capture such dynamic processes. Using longitudinal data, insights can be gained into the nature of the perturbation away from the trajectory of typical development in childhood disorders. Thus, some disorders may reflect a delay in neurodevelopmental trajectories. Our studies in children with attention-deficit/hyperactivity disorder (ADHD) suggest that cortical development is delayed with a rightward shift along the age axis in cortical trajectories, most prominent in prefrontal cortical regions. Other disorders may be characterized by differences in the velocity of trajectories: the basic shape of neurodevelopmental curves remains intact, but with disrupted tempo. Thus, childhood onset schizophrenia is associated with a marked increase during adolescence in the velocity of loss of cerebral gray matter. By contrast, in childhood autism there is an early acceleration of brain growth, which overshoots typical dimensions leading to transient cerebral enlargement. Finally, there may be more profound deviations from typical neurodevelopment, with a complete “derailing” of brain growth and a loss of the features which characterize typical brain development. An example is the almost complete silencing of white matter growth during adolescence of patients with childhood onset schizophrenia. Adopting a longitudinal perspective also readily lends itself to the understanding of the neural bases of differential clinical outcomes. Again taking ADHD as an example, we found that remission is associated with convergence to the template of typical development, whereas persistence is accompanied by progressive divergence away from typical trajectories. Hum Brain Mapp, 2010. © 2010 Wiley-Liss, Inc.