The Adult Autism Quotient (AQ), the Empathy Quotient (EQ) and the Relative's Questionnaire (RQ) were used as part of the Adult Asperger's Assessment (AAA) by a diagnostic service for adults without an intellectual disability with suspected autism spectrum disorder (ASD). This service is part of the National Health Service (NHS) in England. Little is known about the utility of these structured questionnaires despite wide use in clinical practice. It was investigated whether the questionnaires could discriminate between individuals with and without a diagnosis of ASD. Receiver Operating Curve analysis showed good levels of sensitivity to detect a positive diagnosis, but the specificity to exclude those without a diagnosis was poor. A binary logistic regression showed that a combination of the questionnaires also showed limited diagnostic validity. These findings have clinical implications in reviewing the efficiency of the assessment process.