Although it is widely accepted that autism spectrum disorder (ASD) involves neuroanatomical abnormalities and atypical neurodevelopmental patterns, there is little consensus regarding the precise pattern of neuroanatomical differences or how these differences relate to autism symptomology. Furthermore, there is limited research related to neuroanatomical correlates of autism symptomology in individuals with ASD and the studies that do exist primarily include small samples. This study was the first to investigate gray matter (GM) changes throughout the ASD lifespan, using voxel‐based morphometry to determine whether significant differences exist in the GM volumes of a large sample of individuals with ASD compared to age‐ and IQ‐matched typical controls. We examined GM volume across the lifespan in 531 individuals diagnosed with ASD and 571 neurotypical controls, aged 7–64. We compared groups and correlated GM with age and autism severity in the ASD group. Findings suggest bilateral decreased GM volume for individuals with ASD in regions extending from the thalamus to the cerebellum, anterior medial temporal lobes, and orbitofrontal regions. Higher autism severity was associated with decreased GM volumes in prefrontal cortex, inferior parietal and temporal regions, and temporal poles. Similar relationships were found between GM volume and age. ASD diagnosis and severity were not associated with increased GM volumes in any region. Autism Res 2015, 8: 379–385. © 2015 International Society for Autism Research, Wiley Periodicals, Inc.