To induce puberty by transplantation of frozen/thawed ovarian tissue collected prior to gonadotoxic treatment for a cancer. A 9-year-old girl with Ewing sarcoma had one ovary excised and cryopreserved prior to chemo- and radiotherapy. Functional activity of the remaining ovary was destroyed during treatment. Four and a half years later the girl remained pre-pubertal with postmenopausal levels of FSH. Two of ten pieces of frozen/thawed cortex were transplanted to the remaining ovary in order to stimulate puberty. Four months after the transplantation FSH returned to low levels. During the following year puberty gradually progressed to Tanner stage B4 and P3 and regular menstrual cycles started. However, after 19 months the function of the graft ceased. We have shown for the first time in a girl treated for cancer that transplanted ovarian tissue can regain function and secrete estradiol in a sufficient amount to induce puberty. In addition, the majority of her ovarian tissue remains frozen with a possibility to support fertility in adult life. Copyright © 2012 Elsevier Ltd. All rights reserved.