Phenylketonuria is a common amino acid metabolic disorder that is due to a deficiency of phenylalanine hydroxylase in the phenylalanine metabolic pathway, leading to metabolic disorder of phenylalanine in the liver. Phenylketonuria is the first genetic metabolic disorder that can be controlled and treated through diet. Once diagnosed, natural diet should be discontinued for the patient, and a low-phenylalanine diet should be administered. If phenylketonuria is diagnosed and treated early, intelligence can be normal. However, if not controlled, it can lead to delayed growth and development, especially in terms of intellectual development.