Hematologic management of adults with cyanotic congenital heart disease has received little recent attention. The lack of practical therapeutic guidelines prompted us to consolidate our observations on 124 cyanotic adults for general physicians, cardiologists, and hematologists who care for these patients. Specific attention focused on regulation of erythrocyte mass and concepts of compensated and decompensated erythrocytosis, symptoms of deficient tissue oxygen transport, hyperviscosity and iron deficiency, the potential relation between elevated hematocrit levels and brain injury, hemostasis, urate metabolism, and renal function. Cerebral infarction was not seen in any patient. Phlebotomy is best reserved for treatment of symptomatic hyperviscosity. Iron therapy is indicated for symptomatic iron deficient erythropoiesis. Abnormal hemostatic mechanisms are the rule. Antithrombotic medications have little or no role in treatment. Hyperuricemia is the result of abnormal renal uric acid excretion not urate overproduction, and serves as a marker of abnormal renal function. Drugs that promote urate excretion are the preferred maintenance treatment in symptomatic hyperuricemic patients.