Oral estrogens are associated with a two-fold to three-fold increased risk of venous thromboembolism in postmenopausal women. Absolute excess risk is low but higher than for contraceptive pills. Biological data and observational studies suggest that transdermal estrogens are associated with a lower risk for venous thromboembolism than oral estrogens but safety has yet to be proved. Whether addition of progestin plays a significant role is undetermined so far.