Hypotheses concerning the biologic embedding of early adversity via developmental neuroplasticity mechanisms have been proposed on the basis of experimental studies in animals. However, no studies have demonstrated a causal link between early adversity and neural development in humans. Here, we present evidence from a randomized controlled trial linking psychosocial deprivation in early childhood to changes in cortical development from childhood to adolescence using longitudinal data from the Bucharest Early Intervention Project. Changes in cortical structure due to randomization to foster care were most pronounced in the lateral and medial prefrontal cortex and in white matter tracts connecting the prefrontal and parietal cortex. Demonstrating the causal impact of exposure to deprivation on the development of neural structure highlights the importance of early placement into family-based care to mitigate lasting neurodevelopmental consequences associated with early-life deprivation.