To gain further insight into psychosexual functioning, including behaviors, intrapersonal and interpersonal aspects, in adolescents with Autism Spectrum Disorder (ASD), comprehensive, multi-informant measures are needed. This study describes (1) the development of a new measure of psychosexual functioning in both parent- and self-reports (Teen Transition Inventory; TTI) covering all three domains of psychosexual functioning (i.e. psychosexual socialization, psychosexual selfhood, and sexual/intimate behavior). And (2) the initial testing of this instrument, comparing adolescents with ASD (n = 79 parent-report; n = 58 self-report) to Typically Developing (TD) adolescents (n = 131 parent-report; n = 91 self-report) while taking into account gender as a covariate. Results from both informants indicate more difficulties regarding psychosexual socialization and psychosexual selfhood in the ASD group. With regard to sexual/intimate behavior, only parents reported significantly more problems in adolescents with ASD.