Recent advances in the diagnosis and treatment of inborn errors of metabolism have improved substantially the prognosis of many of these diseases, if diagnosed early enough before irreversible damage occurs. This makes it essential that the practicing pediatrician, especially neonatologists be familliar with the clinical presentations and systematic approaches of these disorders. Characteristic clinical presentations, methods of systematic approach and typing of various disorders is discussed in this review. The signs of neurological dysfunctions of many IEMs manifesting in the neonatal period is very nonspecific, such as poor feeding, poor sucking, apnea or tachypnea, vomiting, hypertonia, hypotonia, seizure, letharginess, consciousness change and coma. Many other non-metabolic severe disorders of neonatal period such as neonatal sepsis and intracerebral hemorrhage share these nonspecific symptoms. Hyperammonemia, metabolic acidosis, ketosis and hyperlatic acidemia are observed in many of these conditions but there are exceptions in which conditions all basal laboratory tests are normal, such as NKH, sulfite oxidase deficiency and peroxisomal disorders. According to the results of basal laboratory tests, IEMs in the neonatal period can be categorized in to 6 types. Grouping of IEMs into 6 types will make confirmatory tests and early emergency treatment more efficient.