INTRODUCTION: The epileptic child is three times more likely to have cognitive problems from other neurological pathologies, depending on three facts: the effect exerted by the epilepsy itself, any associated previously-existing neuropsychosocial deficits, and the side effects of the antiepileptic drug (AED). A certain degree of deterioration is universally accepted, although the factors involved in its production are not specified, but are generally accepted as being due to multiple causes. We analyse the relation between neuropsychology and epilepsy in neuropaediatrics. DEVELOPMENT: The relation between epilepsy and behaviour must be seen as the exception rather than the rule, unless there are co-existing personality disorders and/or mental deficiency. The cognitive effects of AED depend on the drug, on the dosages employed and the polypharmacy, and these effects can be both adverse and favourable. The differences observed between one drug and another are open to criticism, although monitored administration of suitable doses generally produces moderate adverse side effects, as evaluated using reliable appraisal methods (MIDDRA). Scaling time in the introduction of the drug is important, especially with some new AED. The mechanisms governing production vary, but an understanding of the mechanism of action improves cognitive functioning thanks to the control over the seizures. In infancy, idiopathic cognitive reactions are produced. The main disorders are a diminished reaction and information processing time with alterations affecting memory, attention and language. CONCLUSIONS: Epilepsy is associated to a number of different, generally moderate, cognitive problems. The age of onset, the type of syndrome, its aetiology, the response to treatment and polypharmacy are multifactorial elements conditioning the side effects. There is a need for batteries of tests capable of forecasting the future and controlling the progression of cognition during treatment. The side effects of AED affecting cognition and behaviour are generally moderate, but they may be important in the case of a particular child.