Summary Background Cancer treatments, including chemotherapy,

radiotherapy, and radical surgery, can induce premature menopause and infertility in hundreds of thousands of women of reproductive age every year. One of the ways to possibly preserve fertility before these treatments is to cryopreserve ovarian tissue for later transplantation. We aimed to restore fertility by cryopreservation and transplantation of ovarian tissue. Methods Ovarian tissue was cryopreserved from a 30-year-old woman with breast cancer before chemotherapy-induced menopause, and this tissue was transplanted beneath the skin of her abdomen 6 years later. Findings Ovarian function returned in the patient 3 months after transplantation, as shown by follicle development and oestrogen production. The patient underwent eight oocyte retrievals percutaneously and 20 oocytes were retrieved. Of the eight oocytes suitable for in-vitro fertilisation, one fertilised normally and developed into a four-cell embryo. Interpretation Fertility and ovarian endocrine function can be preserved in women by long-term ovarian tissue banking