Oral contraceptives have caused little or no overall increase in risk of breast cancer in women in developed countries, even in long-term users or after more than two decades since initial exposure. Limited evidence suggests a possible small increase in risk in users of oral contraceptives in developing countries, and further studies of breast cancer and oral contraceptives in low risk populations are warranted. Oral contraceptives may enhance risk of breast cancer in young women with a history of benign breast disease, and this possibility should also be investigated further. Multiple investigations have fairly consistently shown risk of breast cancer in women under age 45 years to be increased slightly in long-term users of oral contraceptives. Further studies should be conducted to elucidate the mechanism of this apparent phenomenon.