The purpose of this paper is to delineate problems common to all research in the Field of autism and thus, provide a background against which to evaluate the research presented in this special issue of the Journal of Pediatric Psychology. In order to accomplish this, two problems — lack of objective diagnostic specificity and heterogeneity of research poplations — are reviewed and discussed in terms of their implications for basic behavorial and biological research. Finally, a research project aimed at mitigating these problems is briefly discussed.