Objective; To describe a case of isolated membranous obstruction of the inferior vena cava associated with essential thrombocythaemia. Design: A case report concerning thrombosis and its relation to the pathogenesis of inferior vena cava membrane formation. Patient: A 36-year-old woman presented with chronic Budd-Chiari syndrome due to membranous obstruction of the inferior vena cava; the hepatic veins were patent. A diagnosis of essential thrombocythaemia was made concurrently. The membrane was treated by percutaneous angioplasty after medical correction of the thrombocythaemia. The inferior vena cava remains free of obstruction 3 years after presentation and liver function tests returned to normal levels. Conclusion: Membranous obstruction of the inferior vena cava is a rare disorder and may be congenital or acquired. In our patient, we believe that the formation of the membrane was secondary to essential thrombocythaemia. Myeloproliferative disorders and other hypercoagulative states should be considered and actively sought when a diagnosis of membranous obstruction of the inferior vena cava is made.