This review provides an update on the epidemiology of gender dysphoria and transgender identity in children, adolescents and adults. Although the prevalence of gender dysphoria, as it is operationalised in the fifth edtion of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), remains a relatively ‘rare’ or ‘uncommon’ diagnosis, there is evidence that it has increased in the past couple of decades, perhaps reflected in the large increase in referral rates to specialised gender identity clinics. In childhood, the sex ratio continues to favour birth-assigned males, but in adolescents, there has been a recent inversion in the sex ratio from one favouring birth-assigned males to one favouring birth-assigned females. In both adolescents and adults, patterns of sexual orientation vary as a function of birth-assigned sex. Recent studies suggest that the prevalence of a self-reported transgender identity in children, adolescents and adults ranges from 0.5 to 1.3%, markedly higher than prevalence rates based on clinic-referred samples of adults. The stability of a self-reported transgender identity or a gender identity that departs from the traditional male–female binary among non-clinic-based populations remains unknown and requires further study.

The present study reports on the construction of a dimensional measure of gender identity (gender dysphoria) for adolescents and adults. The 27-item gender identity/gender dysphoria questionnaire for adolescents and adults (GIDYQ-AA) was administered to 389 university students (heterosexual and nonheterosexual) and 73 clinic-referred patients with gender identity disorder. Principal axis factor analysis indicated that a one-factor solution, accounting for 61.3% of the total variance, best fits the data. Factor loadings were all ≥ .30 (median, .82; range, .34–.96). A mean total score (Cronbach's alpha, .97) was computed, which showed strong evidence for discriminant validity in that the gender identity patients had significantly more gender dysphoria than both the heterosexual and nonheterosexual university students. Using a cut-point of 3.00, we found the sensitivity was 90.4% for the gender identity patients and specificity was 99.7% for the controls. The utility of the GIDYQ-AA is discussed.