The third versions of the guideline for treatment of people with gender identity disorder (GID) of the Japanese Society of Psychiatry and Neurology does not include puberty-delaying hormone therapy. It is recommended that feminizing/masculinizing hormone therapy and genital surgery should not be carried out until 18 year old and 20 year old, respectively. On the other hand, the sixth (2001) and the seventh (2011) versions of the standards of care for the health of transsexual, transgender, and gender nonconforming people of World Professional Association for Transgender Health (WPATH) recommend that transsexual adolescents (Tanner stage 2, [mainly 12-13 years of age]) are treated by the endocrinologists to suppress puberty with gonadotropin-releasing hormone (GnRH) agonists until age 16 years old, after which cross-sex hormones may be given. A questionnairing on 181 people with GID diagnosed in the Okayama University Hospital (Japan) showed that female to male (FTM) transsexuals hoped to begin masculinizing hormone therapy at age of 15.6 +/- 4.0 (mean +/- S.D.) whereas male to female (MTF) transsexuals hoped to begin feminizing hormone therapy as early as age 12.5 +/- 4.0, before presenting secondary sex characters. After confirmation of strong and persistent cross-gender identification, adolescents with GID should be treated with cross-gender hormone or puberty-delaying hormone to prevent developing undesired sex characters. These treatments may prevent transsexual adolescents from attempting suicide, being depressive, and refusing to attend school. Subsequent early breast and genital surgery may help being employed in desired sexuality.