Self-reported contraceptive histories were obtained at interview from 99 women and compared with prospectively collected data from the Oxford-Family Planning Association cohort study. The effect of different memory aids was evaluated and an assessment was made of the completeness and accuracy of contraceptive histories recorded in general practice notes. Accuracy of recall of total duration of use was sufficiently good to establish the presence or otherwise of a duration-response relationship and could be improved by the use of a contraceptive calendar. Recall of specific brands used was less accurate. In studies where accurate information on use of particular preparations is required, the use of a photo album is recommended, supplemented by data obtained from general practice records to improve the accuracy of dates. General practice records on their own are not sufficiently complete to be used as a sole source of exposure data in studies in which it is important to obtain a complete oral contraceptive history.