Neonatal polycythemia, a venous hematocrit >65%, occurs in 1% to 5% of the total newborn population. Polycythemia can result from an excess production of red blood cells (active form) or from an increase in fetal blood volume (passive form). Clinical manifestations of polycythemia are caused by an increase in whole blood viscosity with a subsequent decrease in blood flow to organ systems. However, little information exists in the nursing literature concerning neonatal polycythemia. This article addresses the two categories of polycythemia and their etiologies; the involved pathophysiology; clinical manifestations of affected organ systems; supportive and specific therapies that can be used to treat polycythemic infants; the prognosis for polycythemic infants; and the difficulty healthcare providers face in deciding whether to treat this disorder. In addition, a case of a symptomatic infant who was treated with a partial exchange transfusion is presented.