In reference to four particular cases where a venous thrombosis associated with the use of oral contraceptives, the authors review the various factors of this problem. The importance of the concomitant use of tobacco as well as risk factors such as hyperlipidemia and hypertension, are especially stressed. These four cases, almost of an experimental nature, permit to correlate precisely the interaction between estro-progestative medications and the occurrence of venous thromboses.