Introduction. Autism spectrum disorders (ASDs) are a group of complex pervasive developmental disorders characterized by impairments in communication, social interaction and behavior. In most cases autism is caused by a combination of genetic factors and environmental risk factors. In 10% to 20% of cases it has been shown that the cause of ASD is genetic. Case Outline. We are describing a 2-year-old boy who was referred to genetic counseling because of speech delay and certain autism-like behavior. By cytogenetic analysis the karyotype 46, inv(X),Y was obtained. The boy was a carrier of a paracentric inversion of the short arm of the chromosome X. After cytogenetic analysis of parental blood, it was detected that mother was a carrier of identical aberration, but had no clinical signs. The method of fluorescent in situ hybridization (FISH) yielded the precise breakpoint in the region (p21.2p11.23). Mother and son were carriers of identical X chromosome. Conclusion. Breakpoints are located in the regions that have already been linked to autism, which indicates that the positional effect of the gene could have been a possible cause of the patient’s genotype. In addition to positional effects, in order to better understand the etiology of autism other genetic and environmental factors should be always taken into consideration. [Projekat Ministarstva nauke Republike Srbije, br. ON175013]