This study determined the licensed and o label' (outside the terms of the licence) use of newly marketed medicines in children (2±11 years) and adolescents (12±17 years), by general practitioners in England. In addition, the incidence rates during the ®rst month of therapy (ID 1 ) for three adverse events, in these groups were compared with those of adults (518 years). The use of these drugs was monitored in 63 individual prescription-event monitoring (PEM) studies, conducted to monitor the safety of these medicines. Patients and drug exposures were identi®ed from dispensed prescriptions. Outcome data (events and demographic information) were obtained from questionnaires. Although only six of these 63 drugs were licensed for use in children, 44 of the 63 drugs were used to treat children. For the majority of the drugs there was no speci®c reference to adolescents in the data sheets therefore it has been assumed that the drugs were licensed for those aged 512 years unless speci®ed otherwise; 55 have been taken as licensed for use in adolescents. Over 690,000 patients were included in the 63 PEM studies, 9081 (1.3%) of these were children and 15,256 (2.2%) were adolescents. 78% of the 9081 children and 93% of the 15,256 adolescents were treated with licensed' drugs. There was a signi®cant dierence in the incidence rate for rash and nausea/vomiting, two adverse events commonly reported during treatment with lamotrigine, between children and adolescents compared to adults. This survey has shown that although only a small proportion (10%) of newly marketed drugs were licensed for use in children the majority of children (78%) were treated with these licensed products but 22% of children received drugs `o label' during the ®rst few years that the drug was marketed and a small number of children and adolescents were given drugs contraindicated in these age ranges.