We report the results of an open trial with lamotrigine (LTG) as add-on drug in children and adolescents with refractory epilepsy and mental delay. Thirty-seven outpatients received LTG for a median period of 7 months at a daily dose of 5 and 15 mg/kg in valproate and non-valproate patients, respectively. The total number of seizures decreased by 100% in eight patients (21.6%) and by >50% in five patients (13.5%). However, the number of seizures remained unchanged in 20 patients (54.1%) and increased in four (10.8%). Lamotrigine was more effective in patients with typical and atypical absences, and in patients affected by atonic seizures. Six children (16.2%) developed generally mild adverse side-effects suggesting that LTG is well tolerated.