This study, the largest longitudinal pediatric neuroimaging study to date, examines the sexual dimorphism in brain development trajectories from ages 3 to 27 years. Using MRI, the researchers found that total cerebral volume peaks at 10.5 years in females and 14.5 years in males. White matter increases throughout this period, with males showing a steeper rate of increase during adolescence. Both cortical and subcortical gray matter volumes follow an inverted U-shaped trajectory, peaking 1 to 2 years earlier in females. These findings highlight the importance of longitudinal data in understanding brain development and the need to consider sex matching in such studies. The study also suggests that the switch from increasing to decreasing gray matter volume may be associated with pubertal maturation, though direct pubertal measures were not available.This study, the largest longitudinal pediatric neuroimaging study to date, examines the sexual dimorphism in brain development trajectories from ages 3 to 27 years. Using MRI, the researchers found that total cerebral volume peaks at 10.5 years in females and 14.5 years in males. White matter increases throughout this period, with males showing a steeper rate of increase during adolescence. Both cortical and subcortical gray matter volumes follow an inverted U-shaped trajectory, peaking 1 to 2 years earlier in females. These findings highlight the importance of longitudinal data in understanding brain development and the need to consider sex matching in such studies. The study also suggests that the switch from increasing to decreasing gray matter volume may be associated with pubertal maturation, though direct pubertal measures were not available.