Gender Reassignment Surgery (GRS) is one part of the treatment that persons who have gender identity disorder, are offered. Endocrine treatment/hormonal treatment is another part. However, the identification of GID and whether (and when) a person with GID is ready for change in his/her sex, is done by a Psychiatrist.
The Harry Benjamin Protocol (now updated to WPATH SOC v7 2011) and various guidelines of Endocrine and Urology societies across the world have reinforced this.
A Psychiatrist would help a person understand, deal and manage his/her gender dysphoria, accept that it is a disorder and discuss what can be done. Since GRS is a major operation, a decision to go ahead with it is usually taken after several meetings and often after life as a member of the opposite sex has been carefully thought off and practiced for at least a year. I would also support you during the transition phase and the post op period when you start your new life.