We report on 2 patients who were apparently normal at birth but later developed characteristics of Wiedemann-Beckwith syndrome (WBS). Both had hypoglycemia neonatally and gradually developed coarse facial changes, umbilical hernia, and macroglossia. Renal sonography done after the macroglossia developed showed large kidneys in both. The placentas were carefully examined in both cases but findings described as typical of WBS were only found in one. The clinical evolution of these infants suggests that some WBS manifestations may have their onset postnatally in some cases. We postulate that the cellular hyperplasia and hypertrophy characteristic of WBS may be caused by persistent rests of embryonal cells that secrete paracrine and/or endocrine growth factors.