Recent epidemiological data indicate that the risk of thromboembolic disease associated with oral contraception (OC) may persist after discontinuation of the drug. It was demonstrated on the other hand that antibodies to sex steroid hormones which develop in OC users, were significantly correlated with the incidence of thrombosis. It is well known that antibodies may persist years after the antigenic stimulation. So it was of interest to see if the eventual occurrence of thrombosis in ex-users might be correlated with the presence of anti-sex steroid antibodies remaining after stopping OC. Thirty-eight women with thrombosis on OC and positive antibody levels, who were required to stop the pill, were followed for periods ranging from 1 to 10 years. No disappearance of anti-ethinyl-estradiol antibodies (anti-EE ab) was observed except for 2 cases. On the other hand, 109 patients with thrombosis either current- (50), past- (29), or never-users (30) of OC were compared to 102 controls of similar groups. Results indicate that the levels of anti-EE ab, and the percentage of women who had anti-EE ab, were similar in those who experienced thrombosis either in the course of OC or after discontinuation. A significant difference was observed between both cases who were current- or ex-users and their controls.