An increased prevalence of autism spectrum disorder (ASD) among children of immigrant backgrounds has been observed but clinical profiles are rarely compared. Diagnostic data from children with ASD notified to the Western Australian Register for Autism Spectrum Disorders were analysed according to maternal-race ethnicity and country of birth. A total of 4776 children aged between 0 and 18 years diagnosed with ASD from 1999 to 2017 were included. Those born to immigrant mothers from lower income countries were younger at the time of diagnosis, had an increased risk of intellectual disability and poorer presentations in the social and communication domains. Further work is required to understand environmental influences that may affect children born to immigrant mothers and to improve monitoring and assessments.