A potential relationship between autism spectrum disorder (ASD) and the use of Assisted Reproductive Technology (ART), which has increased dramatically in recent years, has been suspected—yet existing research has reported mixed findings due to insufficient samples. This project will link an existing population level dataset consisting of all California births between 1996 and 2006 (over five million children, over 60,000 twin pairs, and over 1 million full and half sibling groups) and outcome data on ASD and receipt of developmental services to the CDC's National Assisted Reproductive Technology Surveillance System registry for California infertility clinics for the same period. This detailed dataset from a large ethnically and geographically diverse state will be used to assess the relationship, between Assisted Reproductive Technology (ART), including in vitro fertilization and related procedures, and ASD and to identify the pathways through which any association might operate. This research will identify approximately 50,000 ART births and 24,000 cases of ASD over ten consecutive years, a population sample that overcomes previous limitations and enables an accurate estimation of ASD risk associated with ART. Through this project, investigators will create a unique population- level dataset designed to ascertain any potential association between ART or its subtypes and autism as well as identify the mechanisms of the association. This will better enable individuals and their health care providers to weigh the risks and benefits of ART procedures and to recognize a potentially modifiable risk factor for ASD.