Inborn errors of metabolism are a large group of genetic and biochemical metabolic disorders that are frequently inherited according to Mendel's laws of inheritance, and are caused by mutations in genes encoding certain enzymes or transporters, what is expressed in diseases in the metabolism of carbohydrates, amino acids and fatty acids. The first and the oldest described disease belongs to the group of disorders of amino acid metabolism, and that is alcaptonuria. Considering pathophysiology, there are three groups of disorders, and these are disorders that cause intoxications, such as galactosemia, tyrosinemia, homocystinuria and maple syrup urine disease. Then there are disorders that include energy metabolism, such as disorders of fatty acid oxidation (very-long-chain and medium-chain acyl-CoA dehydrogenase deficiency), carnitine transport, von Gierke disease (glycogen metabolism) and glucose-6-phosphate deficiency (pentose phosphate pathway). The third group are disorders of complex molecules, which include disorders of cellular organelles. Diseases mentioned within the first and the second group are autosomal recessive according to inheritance, except the glucose-6-phosphate dehydrogenase deficiency which is X-linked recessive. To diagnose inborn errors of metabolism, such as disorders in macronutrient metabolism, various biomarkers are used, and these are most commonly metabolites that accumulate due to blockade of a particular metabolic pathway because of deficiency of enzymes or transporters. Depending on the diagnosis, clinical signs and form of the disease, adequate nutritional support is provided.