Research on child development has documented a number of areas in which children, on average, show significant sex differences: gender identity, self-labelling, sex of playmate preference, toy and activity interests, roles in fantasy play etc, etc. These have implications for other aspects of psychosocial development such as interpersonal relational styles, cognitive skills and vocational interests for which there are also significant sex differences. Boys are much more likely than girls to be referred to gender identity clinics and little is known about the longer-term psychosexual outcome of girls. A study of 25 girls between three and twelve attending a gender identity clinic in Toronto followed them up later to see how they were getting on; the girls had to be at least seventeen to participate in the follow-up study. The researchers found that at the follow-up 3 of the girls had Gender Identity Disorder (GID) or gender dysphoria. 8 of the girls were classified as bisexual/homosexual in fantasy and 6 were classified as bisexual/homosexual in behaviour. The remaining participants were classified as either heterosexual or asexual. The rates of GID and bisexual/homosexual orientation were substantially higher than base rates in the general female population. Girls who were more cross-sex typed in their childhood behaviour were more likely to be gender dysphoric at follow up and more likely to have been classified as bisexual/homosexual in behaviour.
Drummond, Kelly D. ... [et al] - A follow-up study of girls with gender identity disorder Developmental Psychology January 2008, 44(1), 34-45