OBJECTIVE Sperm cryopreservation before cancer treatment is the most effective method to preserve the fertility of male patients. We present our 21 years experience with sperm cryopreservation for cancer patients, including an examination of semen quality, the current status of cryopreserved sperm, and the rate of sperm use for assisted reproductive technology (ART). METHODS A total of 721 cancer patients at Fertility Center of CHA Gangnam Medical Center successfully performed sperm cryopreservation for fertility preservation from January 1996 to December 2016. Medical chart review was used to analyze patient age, marital status, cancer type, semen volume, sperm counts and motility, length of storage, and current banking status. RESULTS The major cancers of the 721 patients were leukemia (28.4%), lymphoma (18.3%), testis cancer (10.0%). The mean age at cryopreservation was 27.0 years, and 111 patients (15.4%) performed sperm cryopreservation during or after cancer treatment. The mean sperm concentration was 66.7±66.3 ×10⁶/mL and the mean sperm motility was 33.8%±16.3%. During median follow-up duration of 75 months (range, 1-226 months), 44 patients (6.1%) used their banked sperm at our fertility center for ART and 9 patients (1.2%) transferred their banked sperm to another center. The median duration from cryopreservation to use was 51 months (range, 1-158 months). CONCLUSIONS Sperm cryopreservation before gonadotoxic treatment is the most reliable method to preserve the fertility of male cancer patients. Sperm cryopreservation should be offered as a standard of care for all men planning cancer therapy.