Autism Spectrum Disorder (ASD) affects 1 in 59 children in the U.S., and considerable efforts are being made to understand specific effects on the brain. The cerebellum has a complex role in cognition, behavior, language, and motor function, with these functions being affected in many individuals with ASD. Recent studies of the cerebellum in ASD have conflicting results, potentially based on variation in age, gender, and method of study. Importantly, boys are four times more likely to be identified with ASD than girls. The purpose of this study is to determine whether cerebellar volume in adolescent and young adult males with ASD differs from typically‐developing individuals.We obtained magnetic resonance images (MRI) from male subjects with ASD (N=19) and age‐matched, typically‐developing controls (N=12) recruited through the Thompson Center for Autism and Neurodevelopmental Disorders in Columbia, MO (mean age 15.3 years). We manually segmented whole cerebellar volume from the MRIs using Amira©. Measures of inter‐rater error showed differences of less than 2%. We then compared the two groups using ANCOVA, with age and whole brain volume as covariates. All data collection and recruitment protocols followed IRB approval.Total cerebellar volume is reduced in the males with ASD, by approximately 7% on average, with a strong trend toward statistical significance (p=0.071). These results lend support to the hypothesis that symptoms in some individuals with ASD may be due to cerebellar effects. Given the involvement of the cerebellum in motor coordination and cognitive aspects of language and other behaviors, it logically follows that these functions are affected in many individuals with ASD.Future work will address this hypothesis directly through assessment of the relationship between these structural measures and neurodevelopmental outcomes. Ultimately, our findings may be used as biomarkers for future risk‐factor analysis of co‐morbidities for those with an ASD diagnosis, allowing for early intervention and preventative care.Support or Funding InformationThis project was supported by funding from the IMSD EXPRESS program (NIH R25GM056901), the MU Department of Pathology & Anatomical Sciences, and the Autism Speaks Foundation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.