Phenylketonuria belongs to congenital hereditary metabolic disorders and is caused by enzyme deficiencies in the phenylalanine metabolic pathway. Misdiagnosis of phenylketonuria is not common; if the disease develops, meaning that the child has typical clinical manifestations, it is relatively easy to diagnose. However, once a child exhibits the typical clinical manifestations of phenylketonuria such as blood phenylalanine levels, by the time of diagnosis the child may already have varying degrees of neurological damage, meaning the child might already have intellectual disabilities. Therefore, in such cases, we cannot rely solely on clinical symptoms for diagnosis but should instead carry out newborn disease screening promptly after birth. By diagnosing and treating before any clinical symptoms appear, we can prevent the occurrence of neurological complications, allowing the child to grow and develop like a normal child.