Estimates suggest that by 2010, one in 715 people in the UK will have survived cancer during childhood. With increasing numbers of children cured, attention has focused on their quality of life. We discuss the causes of impaired fertility after cancer treatment in young people, and outline which patients are at risk and how their gonadal function should be assessed. With the report of a livebirth after orthotopic transplantation of cryopreserved ovarian tissue and the continued development of intracytoplasmic sperm injection for men with poor sperm quality, we assess established and experimental strategies to protect or restore fertility, and discuss the ethical and legal issues that arise.