This study describes the initial steps in the development of the 32-item Assessment of Asexual Identity Development Scale (AAID) to measure variables unique to asexuality. Items were developed through a thematic analysis of findings from previous literature and a pilot measure was administered to a sample of expert reviewers for content analysis (n=15). Exploratory factor analysis (n=825) and confirmatory factor analysis (CFA) (n=826) confirmed the dimensionality, reliability and validity of the AAID scale and good model fit was obtained (comparative fit index = .96, root mean square error of approximation = .038, CMIN/DF = 2.20, χ2=1318.84). Six factors emerged: Discovering Asexuality, Being Asexual, Asexual Community, Disclosure, Navigating Relationships and Navigating Relationships: Desires. Standardised factor loadings of all items were high or moderate, and all subscales indicated good to excellent internal reliability (ω = .72–.93). This study supports the internal consistency of the AAID and its subscales, and construct and discriminant validity. Finally, this research demonstrates that AAID scores were stable over five weeks. This measure is a reliable and useful tool to evaluate the development of an asexual identity and will contribute to the growing body of literature on asexuality