Pulmonary veno-occlusive disease is a rare form of primary pulmonary hypertension of unknown aetiology. Four cases were diagnosed in young patients. The diagnosis was suspected on the basis of clinical, radiological, echocardiographic, and catheter evidence and confirmed by taking a lung biopsy sample. In all patients the histology showed obstruction of the pulmonary veins by intimal fibrosis. The clinical course of all patients has been one of progressive deterioration. Although there is no specific treatment for this disease, to establish the diagnosis during life is of great importance in overall clinical management, including counselling the patient and family.