Although self-reported measures are frequently used to assess adults with autism spectrum disorders (ASD), the validity of self-reports is under-researched in ASD. The core symptoms of ASD may negatively affect the psychometric properties of self-reported measures. The aim of the present study was to test the validity and reliability of self-reported data using the NEO personality inventory-revised (NEO-PI-R). Forty-eight adults with ASD and 53 controls completed the NEO-PI-R and a psychiatric interview. Results indicate satisfactory internal consistency of the NEO-PI-R, a satisfactory factor structure, predicted correlations with clinician ratings in the ASD group, and predicted differences in personality between the ASD group and controls. In conclusion, the present results support the use of self-reported measures when assessing adults with ASD.