Diagnosis of autism spectrum disorder (ASD) is currently made when the affected individual is around 2 years of age. Recently, Shen et al. used MRI to scan for brain anomalies in 33 children at high ASD risk and 22 children at low risk, all under 2 years of age. Children who developed ASD (n = 10) had significantly elevated extra-axial fluid compared with non-ASD cases—a finding that was evident as early as 6–9 months of age.