While venous thrombosis and pulmonary embolism are rare among the Chinese, two of nine patients with haemoglobin H disease developed these complications after splenectomy. The clinical data of the two patients were reported and the relevant literature reviewed. It was concluded that the persistent thrombocytosis and an intravascular haemolysis, particularly prominent in this form of thalassaemia, are contributory to the hypercoagulable state.