Learning-impaired children can present with a clinical history suggesting additional problems, including attention deficit disorder and absence seizures. Physicians use clinical judgment in diagnosing the former, but rely heavily on the electroencephalogram (EEG) to diagnose the latter. Most clinicians are reluctant to treat patients with anticonvulsants without seeing 3 Hz spike-and-wave discharges in an EEG. We studied 21 learning-impaired and 7 control children, ages 5 through 12 years, with normal baseline EEGs. All had an additional EEG recorded after 24 hour sleep deprivation. Nine learning-impaired children had a history compatible with absence seizures; 8 of them showed spike-and-wave discharges after sleep deprivation. Of the 12 learning-impaired children with no history of absence seizures, 2 showed spike-and-wave discharges after sleep deprivation. These results are significant (p less than 0.001). Of the 7 controls, none had epileptiform activity following sleep deprivation. Our results show that routine EEGs may be falsely negative in patients with absence seizures, and that sleep deprivation is a potent activator.