The Royal College of General Practitioners' Oral Contraception Study is a continuing cohort survey of the effects of oral contraceptives on the health of users. Neurotic depression is associated with the oestrogen content of combined oral contraceptives, but the risk is small in general, and there is no excess risk associated with oestrogen doses of 35 micrograms or less. It now appears likely that, in the long-term, oral contraceptives are not associated with any increased risk of gallbladder disease, although there is an acceleration of the disease in those women susceptible to it. The progestogen activity of combined oral contraceptives is associated with an increased risk of hypertension and arterial disease. Duration of use no longer seems to influence the occurrence of the latter. Cigarette smoking by oral contraceptive users is the predominant associated risk factor for the occurrence of arterial diseases. Non-smokers using low-progestogen-dose brands may safely use oral contraceptives, probably up to the age of 45 years. In the author's opinion, there is no convincing evidence that oral contraceptive use increases the risk of breast cancer. The evidence for an association with cervical cancer is firmer, but, if confirmed, is unlikely to affect more than one in 3000 users a year. Increased safety in the use of oral contraceptives in future is likely to be achieved through the use of tests which will allow the adjustment of dose to be made to each patient's particular requirements.