Short epileptiform discharges of 10 seconds or less in children with or without epilepsy are not noticed by clinical observation of the child. These so-called subclinical discharges can however disturb cognition and influence daily performance at school and at home. Several studies have been performed to show the negative effect of these epileptiform electroencephalographic (EEG) discharges on choice reaction time tests, short term memory tests (verbal and nonverbal), and on school performance tasks such as reading, writing, and arithmetic. About one-half of children with subclinical discharges will show transient cognitive impairment during these discharges; those with predominantly left-sided discharges are poorer on reading and those with right-sided discharges are poorer on visual spatial tasks. Suppression of the EEG discharges with the antiepileptic drug valproic acid improved cognitive performance in two of six children; failure was because of side effects of the drug or insufficient suppression of the discharges. In individual cases, suppression of the epileptiform EEG discharges can be beneficial. Evaluation of this effect is necessary by standardizing EEG and cognitive performance measures. Furthermore, the phenomenon of transient cognitive impairment (TCI) must be taken into account when evaluating results of psychological tests.