Traumatic brain injury is a leading cause of death and acquired disability in childhood, but the biomechanics of pediatric brain injury are poorly understood. In a porcine model of diffuse brain injury, the anatomic distributions of macroscopic and microscopic injuries were determined following specified inertial (non-impact) rotational loads applied in the axial plane of heads of adult and newborn pigs. The rapid inertial deceleration caused diffuse axonal injury and subdural hematoma in both age groups, but the density and distribution of neural injury was less severe in the immature piglets. These initial data regarding age-dependent injury responses to inertial loads provide a first step towards understanding age-specific mechanisms of head injury.