Occasionally children undergoing cardiac surgery using cardiopulmonary bypass with deep hypothermia and cardiac arrest develop a postoperative syndrome of acute chorea. The authors report the neuropathological findings in two such children surgically treated for congenital heart disease. Examination of the brain showed neuronal loss, reactive astrocytosis and degeneration of myelinated fibers (without frank necrosis) in the globus pallidus, primarily the outer segment, with sparing of other regions commonly susceptible to hypoxic-ischemic necrosis. The localization and relative mildness of the brain damage suggest a susceptibility of the globus pallidus to injury in this setting and implicate disruption of pallidal pathways in the pathogenesis of post-cardiac surgery choreic syndrome.