Studies from the United States have shown increasing incidence of autism spectrum disorder (ASD) with increasing socioeconomic status (SES), whereas in Scandinavian countries, no such relation was identified. We investigated how ASD risk in offspring varied according to parental SES in Taiwan, where we have universal healthcare. Through linking birth reporting data and data from Taiwan’s National Health Insurance program, we studied 706,111 singleton births from 2004 to 2007 and followed them until 2015. Parental SES was determined by monthly salary at the time of childbirth, and child neuropsychiatric outcomes were defined using International Classification of Diseases codes. We identified 7,323 ASD cases and 7,438 intellectual disability (ID) cases; 17% of ASD cases had co-occurring ID. In multivariable Cox regression analysis, higher SES was independently associated with higher risk of ASD after we took into account urbanization levels, child sex, parental age and other covariates. By contrast, higher SES was independently associated with lower risk of ID. Besides the SES disparity in ASD case ascertainment and in the access to healthcare, findings from Taiwan suggest that other social, environmental, biological and immunological factors linked with parental SES levels may contribute to the positive relation of SES and ASD risk.© The Author(s) 2020. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: firstname.lastname@example.org.