It is common practice to forego the prescribing of estrogen replacement therapy (ERT) for patients with a history of breast cancer. The consequences of estrogen deprivation particularly cardiovascular morbidity and osteoporosis are reviewed in the context of the potential risks of ERT in patients with prior breast cancer. The published data regarding breast cancer risks with oral contraceptive use and ERT in healthy women is reviewed. The rationale for a clinical trial of ERT in breast cancer patients, the proposed appropriate patient group and positive end points for assessing benefit of ERT in the population are presented. Lack of reliable clinical data makes ERT in breast cancer patients an unresolved clinical dilemma.