An empirically based 78 question self-rating scale based on DSM-IV-TR and ICD-10 criteria was developed to assist clinicians' diagnosis of adults with autism and Asperger's Disorder-the Ritvo Autism and Asperger's Diagnostic Scale (RAADS). It was standardized on 17 autistic and 20 Asperger's Disorder and 57 comparison subjects. Both autistic and Asperger's groups scored significantly higher than comparison groups with no overlap; sensitivity, specificity, and content validity equaled one. Cronbach's alpha coefficients of internal consistency of three subscales were satisfactory. Gender, age, and diagnostic categories were not significantly associated factors. The RAADS can be administered and scored in less than an hour and may be useful as a clinical scale to assist identification of autism and Asperger's Disorder in adults. The RAADS does not distinguish between autism and Asperger's Disorder.