Background Phthalates are endocrine-disrupting chemicals that influence thyroid hormones and sex steroids, both critical for brain development. Aim We studied phthalate concentrations in house dust in relation to the risks of developing autism spectrum disorder (ASD) or developmental delay (DD). Methods Participants were a subset of children from the CHARGE (CHildhood Autism Risks from Genetics and the Environment) case–control study. ASD and DD cases were identified through the California Department of Developmental Services system or referrals; general population controls were randomly sampled from state birth files and frequency-matched on age, sex, and broad geographic region to ASD cases. All children (50 ASD, 27 DD, 68 typically developing (TD)) were assessed with Mullen Scales of Early Learning, Vineland Adaptive Behavior Scales (VABS) and Aberrant Behavior Checklist.