This study aimed to provide further validity evidence for the dimensional measurement of gender identity and gender dysphoria in both adolescents and adults. Adolescents and adults with gender identity disorder (GID) were compared to clinical control (CC) adolescents and adults on the Gender Identity/Gender Dysphoria Questionnaire for Adolescents and Adults (GIDYQ-AA), a 27-item scale originally developed by Deogracias et al. (2007). In Study 1, adolescents with GID (n = 44) were compared to CC adolescents (n = 98); and in Study 2, adults with GID (n = 41) were compared to CC adults (n = 94). In both studies, clients with GID self-reported significantly more gender dysphoria than did the CCs, with excellent sensitivity and specificity rates. In both studies, degree of self-reported gender dysphoria was significantly correlated with recall of cross-gender behavior in childhood-a test of convergent validity. The research and clinical utility of the GIDYQ-AA is discussed, including directions for further research in distinct clinical populations.