Since the 1950's, cryopreservation of human semen has been recognized as an efficient procedure for infertility therapy, and research has mainly focused on long-term banking of donor semen for artificial insemination (AID). Because assisted reproductive technology (ART) usually employs fresh ejaculate, it is essential to synchronize ejaculation and ovulation. However, if the sperm is efficiently cryo-accumulated, synchronization would not be necessary and much sperm could be provided for fertilization or insemination. In recent years, survival of young males suffering from some cancers has improved due to advanced treatments including high-dose chemotherapy and radiotherapy. However, testicular functions, especially spermatogenesis, are usually sacrificed temporarily or permanently by these treatments. Sperm cryopreservation liberates these patients from iatrogenic infertility and allows them to retain reproductive capability.