Background: Klinefelter syndrome (KS) is the most common cause of genetic male infertility, as most patients present azoospermia. In the testis, a massive decrease in the number of germinal cells is observed and this can begin early in childhood. Thus, it is possible to collect spermatozoa after sperm collection or thanks to testicular sperm extraction (TESE), but the chances finding spermatozoa are decreasing with the age. Sperm collection or TESE should be performed as early as possible. When KS is diagnosed during childhood or teens, fertility preservation could be beneficial. The minimal age for proposing fertility preservation remains controversial and there is no current recommendation about fertility preservation in young men with KS. Design: In this context, we have conducted a systematic review of the results of fertility preservation in young patients with KS to discuss the optimal age range for offering fertility preservation, including or not a TESE. Results: Six articles were included in the systematic review, with patients between 13 to 24 years-old. Except for one, all young men agreed for sperm collection following masturbation. Azoospermia was diagnosed in all patients presenting homogenous KS. One study reported the presence of spermatozoa in the ejaculate of a young man with mosaic KS. Fifty-eight young man for whom ejaculated sperm collection was unsuccessful have benefited from TESE. Testicular spermatozoa were found and frozen in 27 patients out of the 58 (46.5%). The chances of freezing viable testicular sperm between 14 and 23 years of age do not appear to depend on age. Conclusion: Fertility preservation should be proposed in young men, but the optimal age for proposing the first sperm collection could be adapted according to the medical context and the psychological maturity of the young man.