Although common in the neonatal intensive care unit, eosinophilia is often
overlooked or ignored. The latter might be, at least in part, because evalu
ating the neonate with eosinophilia can be a complex process. This article
reviews the physiologic features of eosinophilia, reference ranges, and cli
nical conditions associated with eosinophilia in the neonate. Recommendatio
ns for the evaluation of the neonate with eosinophilia are presented.