SummaryThe authors relate the observation of a 71 years old patient, who presented a severe hemorrhagic disease with bleedings behind the retina and urinary- hemorrhages. The blood clotting tests sustained the diagnosis of prothrombin and proconvertin insufficiency. No information in the history was available about the origin of this deficiency. A very high dicumarol concentration was found in the blood plasma. Four months after the hospitalisation, the authors finally discovered that the patient had received large doses of dicumarol before the appearance of the related symptoms.