The aim of our study was to examine the influence of long term lamotrigine (LTG) add-on therapy on higher nervous function in patients at the developmental age with epilepsy and to analyse the correlation between changes in EEG and cognitive parameters as a consequence of applying LTG in bi- or polytherapy with conventional antiepileptic drugs (AEDs). There were 25 patients (pts), 8-18 years of age with epilepsy stated as "difficult to treat" with partial (12 pts) and generalised (13 pts) seizures. The frequency of seizures was estimated as one or more per month last year (before LTG treatment). The mean age of the patients who had the first seizure was 4.7 yrs. Doses of LTG were adjusted individually (depending on conventional AEDs) according to the recommendation of the producer. The serum levels of conventional AEDs were checked during LTG therapy. Psychological examination was administered three times: before introduction of LTG (as add-on drug) to the therapy, after 3- and after 16 months of the treatment. We measured the level of intelligence, short-term memory, attention, visuomotor integration and abilities of learning. EEG was recorded by Ceegraph (Biologic, USA) after 3 and 12 months of LTG treatment. After the treatment no statistically significant differences in Intelligence Quotient (IQ): global, verbal, nonverbal were noticed. Statistical significance has been stated in parameters of short-term memory. The number of seizures decreased more than 50% in 12 pts. EEG records improved in 6 pts (normalisation of background activity), minimising of epileptform discharges has been noticed in 3 pts. LTG introduced into polytherapy of epilepsy in children and adolescents modified EEG and had minimal influence on cognitive functions.