Objective: The primary objective of this study was to investigate the parenting attitudes towards children with autism spectrum disorders in early childhood in Japan., Design: This study was a cohort study. The participants were enrolled from January 2011 to March 2014. We obtained the prevalence of autism spectrum disorders at 3 years of age, parenting attitudes and other factors from questionnaires. We divided the participants into two groups, an autism spectrum disorders group and a non-autism spectrum disorders group, and compared the parenting attitudes., Setting: This study used data from a Japanese birth cohort study: the Japan Environment and Children's Study, conducted across 15 regional centres in Japan., Participants: The full dataset of the Japan Environment and Children's Study comprised 104 059 records. We excluded 17 889 records because the answer for the autism spectrum disorders in the questionnaire was blank. As a result, we analysed the remaining 82 411 mother-child pairs., Main Outcome Measures: The primary outcome variable was parenting attitudes at 3.5 years of age, which was assessed using a questionnaire. We asked respondents 16 questions related to parenting attitudes, and they answered based on their behaviours. The independent variable was the prevalence of autism spectrum disorders at 3 years of age., Results: Of the 82 411 participants, the children with autism spectrum disorders at 3 years of age were 372 (0.45%). In most questions about parenting attitudes, the autism spectrum disorders group had unfavourable responses. The difference was particularly noticeable when the parents taught their children social discipline. Unfavourable parenting attitudes were 16.6% in the autism spectrum disorders group and 0.8% in the non-autism spectrum disorders group in the question item with the largest difference between the two groups, a significant difference., Conclusions: Parents of children with autism spectrum disorders tended to have unfavourable attitudes, suggesting the importance of parental training., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)