The histories of autism and Asperger's Disorder (AD), based on original contributions by Kanner and Asperger, are reviewed in relation to DSM-IV diagnostic criteria. Their original articles appear to have influenced the distinction between AD and autism made in the DSM-IV. Based on up-to-date empirical research, however, it appears that AD and autism are not qualitatively distinct disorders, but are different quantitative manifestations of the same disorder. The differences between AD and autism may be a function of individual variability in these areas, not the manifestation of qualitatively distinct disorders. The DSM-IV criteria for AD and autism need to be considered with their historical developments, and based on empirical evidence, the DSM-IV diagnostic criteria may be subject to critical review.