Polycythemia vera (PV), a hematologic stem cell disorder characterized by predominant erythroid proliferation, is extremely rare in childhood. Some PV patients develop acute leukemia, especially acute myelogenous leukemia, but cases of PV occurring after treatment of acute leukemia are rare. The authors describe a girl with an atrioventricular canal who was diagnosed with acute lymphoblastic leukemia (ALL) at 23 months of age, was cured with chemotherapy, and developed PV 7 years later. She went on to develop hepatic complications of PV that culminated in death from liver disease at 20 years of age, without recurrence of ALL.