Congenital erythrocytosis (CE) is an extremely rare disease and an infrequent cause of heamoglobin and haematocrit elevation. Genetic testing of CE is not widely available. Patients in whom a cause of erythrocytosis is not identified are classified as idiopathic erythrocytosis (IE) patients. In some types of CE thrombotic events have been reported but there is little hard evidence to advise on management in asymptomatic patients. Similarly is true for patients with IE. We describe a young patient who suffered several thromboembolic complications before the diagnosis of CE type 4 was established.