This paper describes the evaluation and subsequent treatment of a biologic female who presented at age 15 requesting gender reassignment. Multimodality treatment, which continues at the time of writing, has included psychotherapeutic, educational, psychopharmacologic, and endocrinologic interventions. The literature on transsexualism is reviewed, with particular emphasis on the evaluation and treatment of the adolescent girl, and current etiologic theories are discussed. The unique features of adolescence, which complicate the diagnosis and treatment of this disorder, are examined.