Klinefelter Syndrome (KS) is the most common sex chromosomal abnormalities (1/600 newborn males), and is characterized by a hypergonadism hypogonadism. Until few years ago, mostly non-mosaic KS was considered as a model of a complete male infertility although few KS (4-8%) have an oligospermia. Recent studies in adult with non-mosaic KS reported the possibility of sperm retrieval by testicular biopsy (TESE) in around 50% cases and more than some pregnancies have been obtained after TESE with Intracytoplasmic Sperm Injection (ICSI). Since 1997, more than one hundred births are described.