Loss of spermatogonial stem cells can be associated to ageing or can be part of genetic disorders such as 47,XXY Klinefelter syndrome. However, cytotoxic therapies and/or irradiation is the main cause of germ cell loss and can disrupt spermatogenesis temporarily or permanently. These therapies are not only used to treat malignant disorders but may also be used for benign haematological conditions that need bone-marrow transplantation.Since survival rates after cancer treatment are increasing, preservation of the reproductive potential has become an important quality of life issue for both adults but also for childhood cancer survivors. Adult men who cannot bank ejaculate spermatozoa can opt to cryopreserve surgically retrieved spermatozoa, i.e. testicular sperm. Prepubertal boys cannot benefit from sperm banking, but testicular stem cell banking is being introduced into more and more clinics. This strategy should still be regarded as experimental given the lack of any report on successful transplantation and the limited safety data of this method.