Asperger's syndrome (AS), first diagnosed in 1944, and has only recently begun to receive a great deal of research attention. An emerging controversy has been whether AS is a distinct condition from high functioning autism (HFA), and if so, can it be reliably and validly diagnosed. While measures designed specifically to aid in the screening and diagnosis of AS in children have been created, no study to date has appeared which directly tests the utility of AS measures for this purpose. The present study sought to compare the GADS, KADI, CAST and research criteria compiled based on the literature to determine which measure was most accurate at differentiating HFA and AS. Forty children, 14 AS, 11 HFA, and 15 typically developing, were evaluated with respect to their AS symptoms. The GADS had the greatest overall sensitivity and specificity compared to the other AS measures. Differential diagnosis capability of AS assessments varies across instruments. Research criteria may be used to expand upon already existing measures to further define diagnostic symptom patterns. (Contains 4 tables.)