Objective To estimate the risk of developing autism-spectrum disorder (ASD) in children born to immigrants as compared with children of Dutch-born parents. Method Retrospective, population-based cohort study of all live births (n=106953) between 1998 and 2007 in a circumscribed geographical region in the Netherlands. Cohort members were linked to the Psychiatric Case Register to identify diagnosed cases. Results A total of 518 cases of ASD were identified, including 150 children with autism and 368 children with Asperger syndrome or Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS). Children born to migrants from developing countries were at significantly lower risk of ASD [rate ratio (RR)=0.6, 95% confidence interval (CI) 0.5-0.9] than children of Dutch-born parents. Within the ASD group, the risk for the subgroup with Asperger syndrome and PDD-NOS was reduced (RR=0.4, 95% CI 0.3-0.6), whereas that for narrowly defined autism was non-significantly increased (RR=1.4, 95% CI 0.9-2.4). Migrant groups did not differ in age at diagnosis. Conclusion The results echo Swedish findings indicating a reversal of risk gradient in children of parents from developing countries, specifically a decreased risk for high-functioning and increased risk for low-functioning autism.