Fertility is an important issue for cancer survivors. In women, fertility may be directly affected by cancers involving the cervix, uterus and ovaries or by other pelvic tumours. Fertility-sparing surgery holds great hope for certain diseases, for example radical trachelectomy for early-stage cancer of the cervix in young women. The patients at highest risk of infertility are those who have received total body irradiation with chemotherapy, bone marrow transplant conditioning chemotherapy, and pelvic radiotherapy. In women, there are also implications of fertility treatment and pregnancy itself for cancer recurrence. The evidence on unassisted pregnancy after cancer is informed by several large follow-up series. In children and adolescents, no specific test is available to predict future fertility. For men with reduced semen quality after therapy, modern laboratory techniques give a good chance of fatherhood. Services are likely to develop in tertiary centres with reproductive medicine units incorporating the necessary laboratory facilities.