To conduct a prospective follow-up study with 20 treated adolescent transsexuals to evaluate early sex reassignment, and with 21 nontreated and 6 delayed-treatment adolescents to evaluate the decisions not to allow them to start sex reassignment at all or at an early age. Subjects were tested on their psychological, social, and sexual functioning. Follow-up interviews were conducted from March 1995 until July 1999. Treated patients had undergone surgery 1 to 4 years before follow-up; nontreated patients were tested 1 to 7 years after application. Within the treated and the nontreated group, pre- and posttreatment data were compared. Results between the groups were also compared. Postoperatively the treated group was no longer gender-dysphoric and was psychologically and socially functioning quite well. Nobody expressed regrets concerning the decision to undergo sex reassignment. Without sex reassignment, the nontreated group showed some improvement, but they also showed a more dysfunctional psychological profile. Careful diagnosis and strict criteria are necessary and sufficient to justify hormone treatment in adolescent transsexuals. Even though some of the nontreated patients may actually have gender identity disorder, the high levels of psychopathology found in this group justify the decision to not start hormone treatment too soon or too easily.