Phenylketonuria usually requires lifelong treatment, and lifelong treatment is more beneficial to patients. Phenylketonuria is an autosomal recessive disorder, a disorder of phenylalanine metabolism caused by a genetic mutation, which can present with clinical manifestations such as backwardness in mental development, light pigmentation of the skin and hair, and a foul odor of rat urine. The disease is currently incurable and requires long-term treatment by following a low-phenylalanine diet, with regular measurement of blood phenylalanine concentrations and adjustment of recipes according to specific conditions. The disease should be treated as soon as it is diagnosed. The younger the age at which treatment is started, the better the prognosis. Low-phenylalanine diet therapy continues at least until adolescence. Lifelong treatment is more beneficial to the patient. Patients diagnosed with phenylketonuria should actively cooperate with their doctors.