Prevalence report by the Australian Advisory Board on Autism Spectrum Disorders (ASD) estimated that 1 child in every 160 children in the 6-12 year-old age group is affected by ASD. There is no cure for ASD and the causes are not understood. We propose that sex hormones may play a role in the development of these disorders. We will test this hypothesis using knockout and transgenic mouse models which have social interaction deficits and brain structure reminiscent of these disorders.