Inborn errors of metabolism (IEM) are individually rare but collectively common. Approximately 25% of IEMs can have manifestations in the neonatal period. Neonates with IEM are usually healthy at birth; however, in hours to days after birth they can develop nonspecific signs that are common to several other neonatal conditions. Therefore, maintaining a high index of suspicion is extremely important for early diagnosis and the institution of appropriate therapy, which are mandatory to prevent death and ameliorate complications from many IEMs.