Abstract
The diagnosis of autistic spectrum disorders (ASD) is an often-challenging task. Professionals may have difficulty interpreting diagnostic criteria for ASD due to the heterogeneity of the disorder across persons and the change on its symptom presentation within individuals as they mature. In order to assist clinicians in the diagnostic process, numerous rating scales and observational instruments have been developed. This paper will provides in-depth information regarding the most commonly used instruments for the screening or diagnosis of ASD. Reliability, validity, format, and target population will be presented, with the aim of helping clinicians select appropriate measures to assist in the accurate diagnosis of ASD. Future directions with respect to the development of new instruments will be discussed.