Objective: Sperm cryopreservation before gonadotoxic treatment is the basic and most effective method of preserving reproduction, which can be used during adolescence. The communication summarizes 26 years of experience in the operation of an oncological sperm bank, analyzes spermiograms of oncological patients, assesses the relationship between sperm pathology and diagnosis, and determines the number of deaths and the use of frozen sperm. Methods: During the existence of CAR 01 (assisted reproduction center), more than 50,000 spermiograms were performed. From January 1995 to December 2020, a total of 24,729 men were examined within the sperm bank, of which 1,448 (5.9%) had an oncological diagnosis. The spermiograms were evaluated according to current WHO (World Health Organization) manuals. Cryopreservation of sperm has undergone a major development. The rules for the storage of frozen cells have been laid down by Act No. 296/2008 Coll. since 2008. In 2019, the methodology "Cryopreservation of reproductive cells and tissues in patients before cancer treatment" was updated. In all cases, the standard thawing technique was used. The sperms were processed by the swim-up method. As part of the treatment with assisted reproduction methods, oocytes were fertilized by the ICSI (intracytoplasmatic sperm injection) micromanipulation technique. Results: Out of 1,448 examined spermiograms in men with oncological diagnoses, testicular cancer was present in 43.7% of patients and malignant diseases of lymphatic and hematopoietic tissue were found in 24.1%, of which 70,1% included Hodgkin's lymphomas and 29,9% were non-Hodgkin's lymphomas. Leukemia was found in 7.9%, bone and cartilage cancers in 6.8%. The age of the clients of the whole group ranged from 13 to 64 years (27.2 +/- 6.8 years). A total of 38.3% of men had normozoospermia, 54.2% of spermiograms showed pathological findings in 1 to 3 evaluated parameters and 7.5% of patients had azoospermia. Severe asthenozoospermia (mobility <= 10%) was detected in 57.2% of men and severe oligozoospermia (concentration <= 1 x 10(6) mm(3)) in 22.3% of patients. The lowest values of the spermiogram were found in men with testicular cancer; the best values were seen in CNS (central nervous system) cancers. The cryopreservation of sperm was performed in 1,340 cases (92.5%). So far, a total of 160 men (11.9%) have used frozen sperm, of which 6.2% in our center. In these 83 cases, the ICSI technique was always used, 38 clinical pregnancies (45.8%) and 32 births were achieved. We have registered 424 completed storages of semen (31.6%), of which 148 (11.0% of all oncology patients) were made due to death and the others at patients' request. Using the sperm of the dead is a specific issue. Conclusion: In cancer patients, sperm pathologies occur in high percentage. The lowest spermiogram values were found in men with testicular cancer. It is necessary to take into account long-term storage and fertilization by micromanipulation methods. The number of men who die is significantly higher than the number of those who use sperm to treat infertility. Cryopreservation of sperm should be offered to each patient prior to the therapy leading to the destruction of spermatogenesis.