Due to the remarkable improvement in treatments these last decades, long term survival can be expected in more than 80% of childhood cancer patients. Unfortunately, cancer treatments can be harmful to the gonads and can affect reproductive and endocrine functions. While loss of fertility is a major concern for most patients, sperm cryopreservation should be offered to all pubertal male patients. For prepubertal boys, only the experimental option of testicular biopsy in order to cryopreserve testicular stem cells can be proposed.