Issues pertinent to patients with phenylketonuria(PKU) in adulthood are presented. Nutritional management policy that is optimal to prevent such nutritional complications as osteoporosis and possible vitamin B12 deficiency in each age group should be considered. Adolescent girls with PKU and their guardians should be informed of the issue of maternal PKU to prevent the condition. Socioeconomical issues also remain to be solved. Most adult patients have felt that medical expense to continue dietary therapy is a significant economical burden, which often leads to withdrawal from the therapy. Buying life insurance may be refused by insurance companies simply because the patients have PKU. Current knowledge on health status of well-controlled PKU patients should be provided to insurance companies.