"Oral contraception is now one of the most scrutinised medicinal products on the market. Two British investigations that celebrated their 40th anniversaries in 2008 have been major contributors to the evidence base for current clinical practice. Both illustrate the enormous research opportunity of NHS clinical records. The Oxford/Family Planning Association (Oxford/FPA) Study began in 1968, when 17 family planning clinics in England and Scotland started recruiting 17 000 white, married women using oral contraception, the IUD or the diaphragm.3 The Royal College of General Practitioners' (RCGP) Oral Contraception Study started at the same time, with 1400 GPs throughout the UK recruiting 47 000 mainly white, married (or living as married) women, half of whom were using oral contraception. Both studies have followed up their cohorts through a mixture of clinic or practice reports, personal contact, and the cancer and death notification services of the NHS Central Registries. Each study has provided, in different ways, key insights into the effects of different contraceptives; as well as novel information about other women's health issues. For example, the RCGP study was the first to show that the risk of cardiovascular disease is much higher in pill users who smoke,5 especially among older women, and that the risk of hypertension and arterial disease is related to the combined pill's progestogen content.6 The Oxford/FPA study assessed the effectiveness, safety, and return to fertility after stopping different methods. Long-term mortality and cancer results from both studies have been reassuring."