Inborn errors of metabolism (IEM) make up a large group of disorders caused by an inherited defect of proteins that have enzymatic, carrier, receptor or structural roles. The cumulative prevalence of IEM in different populations is around 1:500 – 800 newborns, despite the fact that some of these disorders are extremely rare when taken individually. Early recognition and intervention are essential to avoiding disastrous consequences associated with IEM. The phenotype of IEM patients is very heterogeneous and only in combination with specialized metabolic test it can lead to a correct diagnosis. The aim of the study was defined as evaluation of importance of plasma amino acid profile in the diagnosis of IEM.