The incidence of phenylketonuria in mainland China is similar to that of the West and various estimates include 1:17 000, 1:16 500 and 1:11 186. The exact incidence in China in different regions still has to be clarified. Affected neonates appear normal at birth, with dark hair at birth and vomiting is rare. In infancy and childhood, the fair complexion becomes conspicuous. Head circumference is related to the degree of mental development. We have also observed a "phenylketonuria-like syndrome". These children are mentally retarded with fair complexion but do not have elevated blood phenylalanine levels or urinary ketones. The chances of a second child suffering from this abnormality in 75 high-risk families was found to be 1:3. For treatment, we suggest a low-phenylalanine diet for at least for five years and longer, if possible. Gene analysis has revealed differences in the frequency and composition of mutations in northern and southern Chinese patients.