It has been stated that oestrogen-containing oral contraceptive medication should be discontinued one month prior to surgery, to avoid an increased incidence of post-operative thromboembolism. Others have suggested that the risk of post-operative morbidity is low compared with the risk of pre-operative pregnancy, and that in most cases no such action should be taken. The evidence from clinical investigation is reviewed, with particular reference to study design. It is found that all studies so far conducted are subject to sources of bias or confounding which render their results inconclusive. There is a need for a randomised control trial comparing the effects of discontinuing or continuing oral contraception prior to surgery. Meanwhile, with a post-operative risk inferred but not conclusively demonstrated, if oral contraception is to be withdrawn prior to surgery, great care must be taken to reduce the risk of ensuing pregnancy to as near zero as possible.