Inborn errors of metabolism (IEM) are characterized by the body's inability to convert food into energy. The pathogenetic mechanism is based on defects in a variety of cellular enzymes. In addition to impairment of energy generation, accumulation of substrates may occur, which can deposit in tissue and lead to organ dysfunction. IEM can have profound implications for perioperative management, including difficult airway management, cardiac dysfunction, aspiration risk, seizures, and metabolic dysregulation. For the anesthesiologist, comprehensive knowledge is difficult to attain because of the heterogeneity of this group and the low prevalence of specific diseases. The first part of this article reviews intermediary metabolism, whereas the second part aims to highlight important aspects in perioperative management of patients with IEM. Instead of reviewing each single disorder within the vast group of IEM, we provide a conceptual framework that will facilitate the understanding of main problems encountered in each of the disease subgroups.