Objective: To report the first case of postpartum Budd-Chiari syndrome in a patient with primary thrombocythemia, and to emphasize that serious maternal and fetal complications may occur during pregnancy and postpartum period in patients with primary thrombocythemia. Methods: A pregnant woman with primary thrombocythemia diagnosed during pregnancy was treated with platelet-pheresis and aspirin (80 mg/day) during pregnancy. The course of pregnancy and complications occurring during pregnancy and postpartum period were evaluated. Results: The patient developed oligohydramnios and fetal growth retardation at 32 weeks' gestation. A viable female infant was delivered by cesarean section at 34 weeks' gestation. Hepatic vein thrombosis occurred 3 weeks after cesarean section. The various treatment schedules had no beneficial effect on the course of disease and the patient died 5 months after the diagnosis of hepatic vein thrombosis. Conclusion: Patients with primary thrombocythemia should be followed closely for maternal and fetal complications during pregnancy and postpartum period.