Background Chemotherapy for breast cancer may have a negative impact on reproductive function due to gonadotoxicity. Fertility preservation via banking of oocytes or embryos after ovarian stimulation with FSH can increase the likelihood of a future live birth. It has been hypothesized that elevated serum estrogen levels during ovarian stimulation may induce breast tumour growth. This has led to the use of alternative stimulation protocols with addition of tamoxifen or letrozole. The effectiveness of these stimulation protocols in terms of oocyte yield is unknown. Methods/design Randomized open-label trial comparing ovarian stimulation plus tamoxifen and ovarian stimulation plus letrozole with standard ovarian stimulation in the course of fertility preservation. The study population consists of women with breast cancer who opt for banking of oocytes or embryos, aged 18–43 years at randomisation. Primary outcome is the number of oocytes retrieved at follicle aspiration. Secondary outcomes are number of mature oocytes retrieved, number of oocytes or embryos banked and peak E2 levels during ovarian stimulation. Discussion Concerning the lack of evidence on which stimulation protocol should be used in women with breast cancer and the growing demand for fertility preservation, there is an urgent need to undertake this study. By performing this study, we will be able to closely monitor the effects of various stimulation protocols in women with breast cancer and pave the way for long term follow up on the safety of this procedure in terms of breast cancer prognosis. Trial Registration: NTR4108.