The benefits of estrogen replacement therapy in preventing vasomotor symptoms, osteoporosis, and cardiovascular disease are well documented. Although estrogen is said to be contraindicated in patients successfully treated for endometrial and breast cancer, there are no data to substantiate this admonition. Experience suggests that it can be used safely in patients treated previously for endometrial cancer. Although there is little or no experience with estrogen use in the woman treated previously for breast cancer, circumstantial evidence suggests that it is not contraindicated in all such cases. Informed consent, patient desires, and risk-benefit considerations must enter into the decision to use estrogen in these patients.