The endogenous auditory P300 event-related potential (P3) has been used to differentiate functional and organic cognitive disorders in adults. We found that children with organic cognitive impairments (as determined by the Halstead-Reitan [HR] test) had greater P3 latencies than children with normal HR evaluations. The P3 and HR showed 85% agreement in independent assessments of functional or organically based cognitive impairment in children. Mini-Mental-State, IQ, EEG evaluations, and clinical suspicions of “organicity” with respect to cognitive function were similarly associated with P3 latency.