Girls and young women suffering from a malignant disease that requires treatment with chemo- and/or radiotherapy are at risk of losing fertility. The most significant risk factors are age and type of treatment given. Preserving fertility is of high priority to both the young patient and her parents. This article reviews the effect of chemo- and radiotherapy on gonadal function, and thus fertility, and offers different fertility preserving methods based on the literature. Cryopreservation of ovarian tissue is a possible way of preserving fertility in this group of patients in the future.