Vigabatrin (γ-vinyl gamma aminobutyric acid), a recently developed antiepileptic drug, has been extensively evaluated in the treatment of drug- resistant epilepsy. Several case reports demonstrated that vigabatrin affects urinary excretion of several amino and organic acids. Fourteen children were investigated for the presence of abnormal urinary amino acids before and after treatment with vigabatrin. All demonstrated increased urinary excretion of amino acids, particularly β-alanine, γ-aminobutyric acid, and β- aminoisobutyric acid while on vigabatrin, which were not detected when off medication. These results emphasize the importance of obtaining urine for metabolic evaluation before the administration of vigabatrin.