Fertility preservation is of high importance for patients prior to treatment that can impair fertility. The individual risk of becoming infertile after a fertility-reducing therapy depends on the type and duration of therapy, surgical technique, dose and combination of gonadotoxic drugs or radiation applied, and individual predisposition. Cryopreservation of ejaculated sperm is the standard procedure for creating a fertility reserve in men. In cases of azoospermia or inability to obtain semen by masturbation, testicular sperm can be obtained by (micro-)testicular sperm extraction (TESE) and cryopreserved. In case of retrograde ejaculation, sperm collection can be attempted by rectal electrostimulation or after off-label administration of imipramine from postmasturbatory urine. The cryopreserved sperm can be stored permanently in the gaseous phase of liquid nitrogen before being used in fertility therapy. In Germany, approval according to § 20b of the German Medicines Act (AMG) is a mandatory requirement for performing cryopreservation of sperm and testicular tissue; approval according to § 20c of the AMG must be obtained for use. For prepubertal boys, it is possible to cryopreserve dormant spermatogonial stem cells as part of an experimental procedure.