In 1969 this department reported on 42 women who had developed "idiopathic" venous thromboembolism while using oral contraceptives and 42 women who had developed the disease in the absence of such exposure. We have traced the subsequent history of these women to obtain information about recurrence of the disease.During the follow-up period the risk of recurrence of thromboembolism during pregnancy or the puerperium appeared to be much the same irrespective of whether or not oral contraceptives had been in use at the time of the index attack. Recurrences unassociated with childbearing however, occurred about four times more often among women who had not been using oral contraceptives at the time of the index attack than among women who had been doing so. None of these findings was influenced by the use of oral contraceptives during the follow-up period, since exposure to the preparations was negligible after the index attack.