The validity of Asperger syndrome (i.e., apart from high-functioning autism) continues to be the topic of considerable debate. Consistent with Asperger's original description of the condition there appear to be some important potential differences from autism if both conditions are strictly defined. Although the importance of genetic factors in the transmission of autism is increasingly clear it also appears that genetic factors may play an even more important role in Asperger syndrome (AS). The nosological validity of this condition and its relation to the various PDD spectrum disorder remains an important topic for future research. Well-designed and carefully controlled studies are needed in which patterns of comorbidity and associated problems in family members can be carefully assessed. Such studies will contribute to our understanding of the relationship of AS and autism and may clarify important genetic mechanisms of relevance to autism.