The aminoacidopathies constitute the biggest group of inborn errors of metabolism, keeping growing in number, considering the amount of metabolic chains envolving the aminoacids in the human economy. The author try to presente an up to date classification of the main aminoacidopathies which determine neurological and/or mental symptomatology. As a next step, are presented a review on the main diagnostic methods, pointing out where some methodology fail. Some particularities in phenylketonuria, maple syrup and propionic aciduria, concerning to the genetic variation are reviewed. Finally, two aminoacidopathies recently described are presented: the pyroglutamic aciduria and the beta-methyl-crotonyl-CoA-carboxilase deficiency.