Several recent studies have shown that blood pressure may increase during oral contraceptive (OC) use; according to published figures, the incidence of this condition ranges from 0% to 15.5%. A 1974 Royal College of General Practitioners (RCGP) study showed that women using OC with 50 mcg of estrogen and more than 3 mg of norethindrone acetate had 1.4 times the incidence of hypertension than women receiving the same dose of estrogen but less than 3 mg of progestogen. The RCGP study also indicated a relationship between duration of treatment and incidence of hypertension, and between age and blood pressure elevation. Numerous investigations have been carried out to observe the etiology of hypertension, with different and conflicting results. It clearly appears that changes occur in the renin-angiotensin system; more specifically, plasma renin serum substrate is increased, and is associated with an increase in plasma renin activity; results of this interrelationship depend on dose and proportion of specific estrogen and progestogen, duration of use, and individual response. Other possible etiological factors involve the sympathetic nervous system, the alteration of prostaglandin synthesis, changes in the pituitary adrenal axis, and in blood dynamics; a possible genetic predisposition to hypertension must also be taken into consideration. Hypertension is strictly related to cardiovascular accidents; according to a RCGP study women using OC have 5 times greater risk of death from cardiovascular causes, or 26.8/100,000 mortality rate as opposed to 5.5/100,000 in nonusers. At present the only factor predicting OC-induced hypertension is previous development of hypertension while under OC treatment; women using OCs should be carefully and regularly checked. Since both estrogen and progestogen seem to be responsible in the etiology of hypertension the lowest possible dosage of OC should be chosen. Hypertensive patients should discontinue OC use and be encouraged to use other forms of contraception, since fetal and maternal mortality are increased during pregnancy in hypertensive women. None of the many studies conducted on the incidence of hypertension and cardiovascular mortality and morbidity in postmenopausal women under estrogen therapy have demonstrated changes in the incidence of such accidents.