The transition to postsecondary education is characterized by many changes for adolescents with autism spectrum disorder (ASD). A data-based understanding of a student's readiness for postsecondary education could help students, and their parents, better prepare for this life transition. The Transition Readiness Scale (TRS) was created to address this need. The TRS is a self/other-report questionnaire used to assess postsecondary readiness across behavioral, cognitive, and emotional domains among adolescents 15-18 years of age. The present study details measure development and provides preliminary psychometric properties in a sample of transition-aged youth with ASD. Results indicate strong internal consistency, adequate item-level analyses, and discriminant and concurrent validity. Future validation of the TRS in large-scale field testing is merited to inform clinical interpretation.