This review describes the current situation with regard to diagnostic instruments for Asperger syndrome. The paucity of such instruments, and the lack of adequate standardisation data amongst the few that do exist, represent a serious omission for both clinicians and researchers. The major problem limiting the development of effective diagnostic or screening instruments is the confusion inherent in ICD-10 and DSM-1V systems in differentiating autism from Asperger syndrome. In the absence of clear and clinically satisfactory diagnostic criteria, efforts to develop valid assessment instruments may be attempting to put the horse before the cart!