High dose chemotherapy and radiotherapy have radically increased long-term survival of young cancer patients, but major side effects of these treatments are ovarian failure and infertility. Knowledge of the risks and probabilities of ovarian failure caused by treatment is crucial for patients and physicians in order to make informed choices that will best serve patients' interests. This review presents data on ovarian damage and failure following exposure to radiotherapy, chemotherapy and ablative therapy. The risk is evaluated from the published literature according to patient's age, treatment protocol and also according to the diagnosis of some common malignancies. Many of these patients will not be sterilized immediately following treatment, but will suffer from premature menopause. In order to prevent sterilization, ovarian transposition before pelvic irradiation is mandatory. Besides cryopreservation of ovarian tissue and embryos before administration of chemotherapy, the possible protective effect of pituitary-ovarian down-regulation is discussed. The mechanism of primordial follicles damage induced by radio/chemotherapy is presented as well as the role of apoptosis signalling pathways underlying destruction. Increased knowledge of these mechanisms could help to identify potential effective inhibitors that can block the path of primordial follicles destruction and reduce ovarian failure rate.