Prader-Willi syndrome (PWS) is a genetic syndrome caused by the lack of expression of imprinted genes located on paternal chromosome 15q11-q13, characterized by endocrine defects, an insatiable appetite, short stature, cognitive and behavioral difficulties and dysmorphic features. Nearly all PWS males and most PWS women show clinical and/or laboratory evidence of hypogonadism, affecting their habitus, health and quality of life. Until recently, hypogonadism in PWS was generally considered to be of centrall, hypothalamic origin. However, recent studies have shown that primary gonadal dysfunction is the major contributor to hypogonadism in this condition, while severe gonadotropin deficiency is rare. Despite clinical and laboratory evidence of hypogonadism, young adult PWS men and women have sexual and romantic interests and aspirations. Pregnancies have been reported in a few women with genetically documented PWS. Fertility has not been reported in PWS men. Recognition of these interests is essential for physicians and caregivers in order to offer proper anticipatory guidance, psychological and sex education and counseling. Individual variations in pubertal development, reproductive hormone profiles, bone-mineral density and individual appeal need to be considered when recommending sex hormone replacement in this population. Testosterone should be considered in most hypogonadal PWS males, considering possible side effects. Hormone replacement may be indicated in PWS women with decreasing bone mineral density or in PWS women who wish to have regular menses. Contraception should be considered in women with normal inhibin B levels. Hormone replacement is likely to improve bone density, quality of life and body image.