Real-time cranial ultrasonography (cranial sector [CS] scan) was prospectively evaluated for its usefulness in identifying irreversible cerebral injury in critically ill children admitted to the neonatal and pediatric ICUs at our institution. Absence of pulsatile movement of the anterior and middle cerebral arteries was determined to represent absent cerebral perfusion and thus profound irreversible injury. Of 800 consecutive patients representing 1900 CS scans, 12 met the criteria. Six were neonates and 6 were older infants. Mechanisms of injury included severe hypoxia, head trauma, and CNS infection. Absence of brain function by clinical examination and EEG confirmed CS findings in 11 who expired. One neonate survived with intact brainstem function but no identifiable cerebral function or growth. No false positives were demonstrated. We found the CS scan to be a reliable bedside adjunct in the determination of irreversible cerebral injury or cerebral death.