Individuals severely affected by autism tend to be underrepresented in research studies. To address this need, the Autism and Developmental Disorders Inpatient Research Collaborative (ADDIRC) is performing the Autism Inpatient Collection (AIC) study. Directed by SFARI Investigator Matthew Siegel, this ongoing multisite effort is enrolling children and adolescents admitted to any of six specialized inpatient psychiatry units. Enrollment began in March 2014 and continues at a rate of more than 400 children annually. Preliminary data published in this paper indicate that the AIC has a rich representation of understudied and underrepresented autism populations, serving as a substantial new resource for studying the behavioral and biological bases of severe autism. The AIC welcomes collaborations with other investigators. Access to phenotypic data and biosamples may be requested through SFARI (contact [email protected] for more information). An online participant community, AIC@IAN, has also been formed to help researchers stay in touch with families participating in this study.