Transient nonketotic hyperglycinemia is characterized by clinical and biochemical findings similar to those seen in classic nonketotic hyperglycinemia. Abnormalities in amino acids are partially or completely resolved in a period ranging from days to months. Almost all patients with the classic form of nonketotic hyperglycinemia survive with severe neurologic sequela, whereas most of the patients with the transient form exhibit normal development. Therefore, distinguishing the transient form of nonketotic hyperglycinemia from classic nonketotic hyperglycinemia is important to predict outcome of the patients. Transient nonketotic hyperglycinemia has been reported in only seven neonates. This article adds two cases to the transient nonketotic hyperglycinemia and reviews the relevant literature. Common clinical features were determined, and presence of miotic pupils was stressed.