The purpose of this study is to document the content and accuracy of middle school students’ spontaneously generated definitions of autism in order to inform future peer education interventions. Authors evaluated 450 middle school students’ written definitions of autism for accuracy and content. Most students (n = 321; 71.3%) provided accurate definitions of autism; the remaining definitions consisted of (a) a combination of accurate and inaccurate information (n = 45; 10.0%), (b) reporting “Don’t know” (n = 43; 9.6%), (c) inaccurate information (n = 20; 4.4%), and (d) combinations of uncertainty in the presence of accurate and inaccurate information (n = 21; 4.6%). Accurate responses reflected only basic understanding that autism was a disability; few accurate responses identified social, communicative, or restrictive patterns of behavior as core difficulties for individuals with autism. Middle school students reported inaccurate information across varied content, such as etiology, core symptoms, and associated problems. Results suggest that peer education messages should highlight information regarding the defining features, etiology, consequences, and outcomes related to autism.