The Gender Identity Development Service (GIDS), based at the Tavistock and Portman Trust in North London, was set up initially to provide―for the most part―talking therapies to young people who were questioning their gender identity. But in the last decade GIDS has referred more than a thousand children, some as young as nine years old, for medication to block their puberty. In the same period, the number of young people seeking GIDS's help exploded, increasing twenty-five-fold. The profile of the patients changed too: from largely pre-pubescent boys to mostly adolescent girls, who were often contending with other difficulties. This urgent, scrupulous and dramatic book explains how, in the words of some former staff, GIDS has been the site of a serious medical scandal, in which ideological concerns took priority over clinical practice.