Ischemia/reperfusion injury to the developing brain is a major cause of neurologic abnormalities in preterm infants. To investigate the underlying mechanisms, we modified a previously described rat model of unilateral uterine-artery ligation on the 17th embryonic day (E17). Growth retardation was taken as an index of in utero ischemia, and pups born with a birth weight more than 2 standard deviations below that of controls were compared with the same-litter, normal-growth control pups born from the nonligated horn. Prenatal ischemia probably associated with hypoxia and followed by reperfusion at birth induced white matter damage at a developmental stage corresponding to extreme prematurity in humans. On P0 (day of birth), growth-retarded pups exhibited lesions in the cingular white matter and internal capsule with increased counts of activated microglial cells for 2 weeks compared with controls. Astrogliosis was detected in the injured white matter. On P3, increased apoptotic cell death was seen in O4-positive preoligodendrocytes, which were abnormally scarce on P7. Defective myelination, as assessed by myelin-binding-protein labeling, was detected until adulthood. The diffuse white matter damage in growth-retarded rats replicated the main features of white matter damage in human preterm infants.