Before the age of 14 years, 1% of the paediatric population will develop a seizure. The only systematically required complementary examination is an electroencephalogram (EEG). Additional biological or radiological examinations depend on the circumstances, the past medical history of the patient and other associated symptoms or clinical signs. A seizure can be the first sign of acute intoxication and represents a severity criterion. Failure to detect the toxic cause of a seizure can lead to a delay in the access or administration of an antidote if applicable. This can lead to target organ toxicity due to the absence of specific treatment. In the current French guidelines for a first seizure, a toxicological analysis is recommended if there is a possibility of exposure to toxic medications or products. However, this screening is often missing, unless a witness suggests that the child may have been exposed to a toxin.The recognition of a paediatric toxidrome is low among paediatricians, paediatric neurologists or emergency physicians. This is due to a lack of knowledge in clinical toxicology and the screening for toxic aetiology is not frequently or irrelevantly prescribed. There is an increasing number of proconvulsive molecules on the market. These molecules are not targeted in classic toxic screening. As result, a toxic cause of a seizure may be missed unless specific screening is performed. For all these reasons, little is known about the prevalence of toxic causes after a first episode of non-febrile seizure and probably under estimated in the paediatric population, especially in young children. New technologies for toxic detection like chromatography combined with mass spectrometry allow wide screening on different matrix. Initially dedicated to forensic analysis, they are more widely accessible for the exploration of the patients. The CASTox study is based on this context.