A total of 11 children with attention deficit disorder (ADD) and nine control children performed a continuous performance test (CPT) of the A-X type with concurrent neuroelectric brain mapping to assess preparatory processing, purportedly mediated by the frontal lobes. This cued CPT task proved to be a highly specific task. The groups could be clearly differentiated both at the behavioral and electrophysiological level. ADD children detected fewer signals and made more false alarms. There were no major group differences in topographical distribution of the event-related potential microstates, but ADD children displayed reduced global field power (GFP) in an early CNV/P3 microstate to cues. This indicated that impaired orienting to cues, rather than impaired executive target processing, determines the initial processing stages in ADD. In comparison with data from the same task run in Utrecht, the same orienting deficit in clinically diagnosed ADHD children was demonstrated. Low resolution electromagnetic tomography (LORETA) estimated posterior sources underlying these orienting processes and the orienting deficit. This argued against frontal lobe involvement at this stage and suggested involvement of a posterior attention system.