A meta-analysis of 55 fMRI studies on Attention-Deficit/Hyperactivity Disorder (ADHD) reveals significant brain dysfunction in multiple large-scale neuronal systems. In children, ADHD was associated with hypoactivation in the frontoparietal and ventral attention networks, and hyperactivation in the default, ventral attention, and somatomotor networks. In adults, hypoactivation was mainly in the frontoparietal system, while hyperactivation was found in the visual, dorsal attention, and default networks. These findings suggest that ADHD-related dysfunction is not limited to specific brain regions but involves broader networks involved in executive functions, attention, and sensorimotor processes. The results were consistent across different age groups, clinical characteristics, and neuropsychological tasks, even in the absence of comorbid mental disorders or stimulant treatment history. The study highlights the importance of considering large-scale brain networks in understanding ADHD pathophysiology, moving beyond traditional models focused on isolated brain regions. The findings support the idea that ADHD involves altered connectivity within and among neural networks, rather than isolated abnormalities. The study also notes that ADHD-related hyperactivation in the default network may be related to impaired task-related deactivation, and that compensatory mechanisms, such as hyperactivation in visual regions, may be present in some cases. However, the study did not find significant differences in regions related to motivation and emotion, such as the ventral striatum, orbitofrontal cortex, or amygdala/hippocampus. The study also highlights the limitations of fMRI data, including the inability to define an absolute baseline state of activation. Overall, the results suggest that ADHD is a disorder involving dysfunction in multiple large-scale brain networks, and that future research should focus on understanding the interplay among these networks and their links to ADHD symptoms.A meta-analysis of 55 fMRI studies on Attention-Deficit/Hyperactivity Disorder (ADHD) reveals significant brain dysfunction in multiple large-scale neuronal systems. In children, ADHD was associated with hypoactivation in the frontoparietal and ventral attention networks, and hyperactivation in the default, ventral attention, and somatomotor networks. In adults, hypoactivation was mainly in the frontoparietal system, while hyperactivation was found in the visual, dorsal attention, and default networks. These findings suggest that ADHD-related dysfunction is not limited to specific brain regions but involves broader networks involved in executive functions, attention, and sensorimotor processes. The results were consistent across different age groups, clinical characteristics, and neuropsychological tasks, even in the absence of comorbid mental disorders or stimulant treatment history. The study highlights the importance of considering large-scale brain networks in understanding ADHD pathophysiology, moving beyond traditional models focused on isolated brain regions. The findings support the idea that ADHD involves altered connectivity within and among neural networks, rather than isolated abnormalities. The study also notes that ADHD-related hyperactivation in the default network may be related to impaired task-related deactivation, and that compensatory mechanisms, such as hyperactivation in visual regions, may be present in some cases. However, the study did not find significant differences in regions related to motivation and emotion, such as the ventral striatum, orbitofrontal cortex, or amygdala/hippocampus. The study also highlights the limitations of fMRI data, including the inability to define an absolute baseline state of activation. Overall, the results suggest that ADHD is a disorder involving dysfunction in multiple large-scale brain networks, and that future research should focus on understanding the interplay among these networks and their links to ADHD symptoms.