Disorders of Sex Development (DSD) remain a fascinating challenge for the paediatricians, endocrinologists, biologists, psychiatrists, geneticists, radiologists, surgeons and for the whole society. This article aims at highlighting the current controversies and questions met with genital reconstruction in children born with abnormal genitalia. The main current techniques of masculinization and feminization are reviewed with their progress and their problems. The tools of decision used to assign a gender in some newborns with complex DSD are discussed showing that at the dawn of the third millenium, one still does not know why a boy is a boy, and a girl is a girl.