Abstract  The most widely used and influential typologies for transsexualism and gender identity disorder (GID) in adolescents and adults
employ either sexual orientation or age of onset of GID-related symptoms as bases for categorization. This review compares
these two typological approaches, with the goal of determining which one should be employed for the diagnosis of GID in Adolescents
or Adults (or its successor diagnosis) in the forthcoming revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM). Typologies based on sexual orientation and age of onset of GID-related symptoms are roughly comparable in ease and
reliability of subtype assignment. Typologies based on sexual orientation, however, employ subtypes that are less ambiguous
and better suited to objective confirmation and that offer more concise, comprehensive clinical description. Typologies based
on sexual orientation are also superior in their ability to predict treatment-related outcomes and comorbid psychopathology
and to facilitate research. Commonly expressed objections to typologies based on sexual orientation are unpersuasive when
examined closely. The DSM should continue to employ subtypes based on sexual orientation for the diagnosis of GID in Adolescents
or Adults or its successor diagnosis.