The regular medical surveillance provided to oral contraceptive (OC) users, which allowed early diagnosis or even prevention of some serious disorders, was recognized as 1 of the primary benefits of combined OCs from their earliest use. Another benefit is protection against functional ovarian cysts resulting from the suppression of pituitary hormone secretion. Combined OCs can be used to treat polycystic ovarian dystrophy. It now appears clear on the basis of extensive epidemiological study that OCs afford protection against epithelial cancer of the ovary. The relative risk of ovarian cancer is .4 to .6 for women using OCs relative to women who have never used them. The protective effect appears to begin after 2-3 years of use, to persist for several years after termination of use, and to be independent of the formulation used. As with functional cysts, the protective effect of OCs against ovarian cancer appears to depend on the suppression of ovulation and inhibition of follicle stimulating hormone and luteinizing hormone secretions. Synthetic estrogens and progestins have the same effects on the target tissues as do the endogenous hormones. A true inhibition of ovarian secretions and a balance between the estrogen and progestin are needed to prevent hyperplasia or atrophy of the breast and endometrium. Use of low dose progestins is often associated with incomplete inhibition of gonadotrophins and relative hyperestrogenism, while sequential pills are too strongly dosed in estrogen and also lead to hyperestrogenism. Otherwise, combined pills often provide a more stable hormone balance than that found in spontaneous cycles. A well chosen combined pill can be used to treat premenstrual syndrome, regularize cycles, and protect against benign breast disease. Most epidemiological studies have concluded that use of combined OCs is without influence on the relative risk of breast cancer. Contraindications based on individual or family medical history must however be respected and OC users should receive careful periodic surveillance. OC users have 2 times less risk of endometrial cancer than nonusers. The protective effect appears after 12 months, apparently persists for 15-20 years after termination of use, and is provided by combined OCs at standard or low doses. New pill formulations are being sought which have fewer metabolic and vascular effects without loss of the protective effects of standard dose pills. Low dose pills containing currently used progestins have been accused of providing incomplete ovarian inhibition. A triphasic OC containing the new progestin gestodene offers the strong antigonadotrophic effect of gestodene along with a good balance between the estrogen and progestin. It appears reasonable to expect that this triphasic will offer the same protection against ovarian and endometrial cancer as more strongly dosed OCs.