OBJECTIVE: The present study aims to investigate potential differences in cerebral blood flow between children with Cognitive Disengagement Syndrome (CDS) and those with Attention Deficit Hyperactivity Disorder (ADHD) using Doppler ultrasound. METHODS: In this single-center prospective study, we included 24 cases in the ADHD group with CDS symptoms, 29 cases in the ADHD group without CDS symptoms and, 26 children in the healthy controls. The children ranged in age from 6 to 15. Participants were evaluated by diagnostic interviews and standardized measures. Doppler ultrasound was performed to measure peak systolic velocity and blood flow volume (BFV) in the internal carotid (ICA) and vertebral arteries for each participant. RESULTS: The right ICA and total ICA BFVs were significantly lower in the CDS group compared to the ADHD and control groups (p = 0.007 and p = 0.003, respectively). In addition, there was a weak negative correlation between right ICA BFV and CDS scores, suggesting a possible link between reduced cerebral blood flow and CDS symptom severity. CONCLUSION: This study provides a noteworthy starting point for research on the neurovascular basis of CDS. Our findings indicated significant differences in cerebral blood flow between CDS and ADHD, supporting the idea that CDS is a unique attentional disorder with distinct neurobiological characteristics from ADHD.