Asperger's syndrome has gained tremendous recognition and popularity in the last 20 years. However, controversy around the nature of the disorder, whether it is distinct from high functioning autism, and whether it can be reliably and validly diagnosed has continued throughout this period unabated. Fortunately, there has been a strong tradition of developing systematic data based methods of differential diagnosis in the autism spectrum disorders. The bulk of the effort has been in autism, but there has been moderate, yet consistent efforts to develop data based methods to diagnose Asperger's syndrome as well. The present paper provides an up to date critical review of the existing literature on the topic. Strengths, weaknesses of the research, and avenues for future efforts are discussed.