The first case study of identical male twins concordant for DSM-IV Asperger's disorder (ASD) was presented. Their monozygocity was confirmed by short tandem repeat analyses with a probability of 99.999963%. Despite sharing the same DNA and environment, the twins are different in comorbidity (i.e., major depressive disorder in the elder and absence seizure in the younger) and in IQs and motor performance (i.e., the elder was lower in IQs and clumsier). Both of them were normal in computed tomographic scanning and magnetic resonance imaging discordant with some previous reports of brain imaging abnormalities in ASD. Further studies are needed to clarify inherited/acquired epigenetic defects and brain imaging abnormalities relating to behavioral phenotypes in ASD twins.