The neonatal polycythemia/hyperviscosity syndrome continues to perplex the pediatrician. Although it is reasonably common, with an incidence of 1% to 5%, significant symptoms are less frequent and may be more due to predisposing factors such as perinatal asphyxia, intrauterine hypoxia, or hypoglycemia. Infants who are small for gestational age or affected by maternal gestational diabetes are at high risk for the disorder. Partial exchange transfusion used to lower hematocrit will decrease viscosity, reverse many of the physiologic abnormalities, and ameliorate most symptoms, but has not been shown to significantly impact the long-term outcomes of these children.