OBJECTIVE: To review the use of hormonal replacement therapy (HRT) after treatment of breast cancer. OPTIONS: The effect and role of estrogens on breast cancer. OUTCOME: Improved health and quality of life for women with breast cancer. VALUES: References were collected through MEDLINE searches up to 2002. EVIDENCE: The level of evidence and quality of recommendations have been determined using the criteria described by the Canadian Task Force on the Periodic Health Examination. BENEFITS, HARMS, AND COSTS: Utilization of the information to make proper risk-benefit assessment of HRT use in women with breast cancer. RECOMMENDATIONS: 1. HRT after treatment of breast cancer has not been demonstrated to have an adverse impact on recurrence and mortality. (II-2B). 2. HRT is an option in postmenopausal women with previously treated breast cancer. (II-2B). 3. Prospective, randomized clinical trial results are needed. (III-A). VALIDATION: Recommendations were viewed and revised by the Breast Diseases Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and approved by the Executive and Council of the SOGC. SPONSOR: The Society of Obstetricians and Gynaecologists of Canada.